Hello and welcome to Sports Mole's live text coverage of the Europa League semi-final first leg between Arsenal and Valencia at the Emirates Stadium.

The Gunners beat Napoli 3-0 in the quarter-finals to make it to this stage for the second season running, but they have lost all three league games since then to put added importance on tonight's match.

Los Che, who eased past domestic rivals Villarreal in the last round, are also out of form domestically speaking as they have lost back-to-back matches to find themselves outside of the top four in La Liga.

ARSENAL TEAM NEWS!

STARTING XI: Cech; Mustafi, Koscielny, Sokratis; Maitland-Niles, Guendouzi, Xhaka, Kolasinac; Ozil; Aubameyang, Lacazette

SUBS: Leno, Monreal, Torreira, Elneny, Mkhitaryan, Iwobi, Nketiah

VALENCIA TEAM NEWS!

STARTING XI: Neto; Roncaglia, Gabriel, Garay, Diakhaby, Gaya; Piccini, Soler, Parejo, Guedes; Moreno

SUBS: Domenech, Lato, Wass, Santi Mina, Ruben Sobrino, Torres, Gameiro

KICKOFF:  Arsenal show four changes from their 3-0 loss to Leicester City at the weekend, with Ozil and Guendouzi - who sat out both legs against Napoli - being brought into the starting lineup. Valencia also show four alterations from their most recent outing. The Gunners get us up and running here!

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Lacazette gets the wrong side of Roncaglia with less than a minute on the clock. The Valencia defender puts his hand on his opponent, but Lacazette made the most of the contact in the box.

The home side have started the brighter of the two sides. Valencia have named a very defensive side this evening, perhaps knowing that Arsenal have relied on goals at the Emirates Stadium to get them this far. The return fixture will be played at Mestalla next Thursday, incidentally.

Los Che have started this match exactly as predicted - getting everyone back behind the ball to keep Arsenal out. The visitors enjoyed a rare attack forward a few moments ago, but it came to an abrupt end as Sokratis caught Diakhaby. That should have been a yellow card.

Diakhaby is back on the field. It is no wonder he stayed down following the challenge from Sokratis - the Arsenal defender caught him right on the ankle and got none of the ball. Valencia are about the swing the ball into the box.

CHANCE!  Valencia's well-worked free-kick routine nearly pays off. Rodrigo drifts into some space at the back post, profiting from Arsenal's high line, and sends a first-time pass into the six-yard box. None of his teammates could help it over the line, though, as the Gunners clear their lines.

Replays show that it was not an Arsenal player that cleared Rodrigo's delivery a minute or so ago - Garay simply failed to convert from pretty much under the crossbar! That is a shocking miss.

GOAL!  ARSENAL 0-1 VALENCIA (MOUCTAR DIAKHABY)

Arsenal's defensive deficiencies have once again cost them as Valencia take the lead early on. Moments after that shocking miss from Garay, teammate Diakhaby made no mistake from a similiar position as he outjumped three Arsenal players to knock Rodrigo's headed pass over the line. The corner was not dealt with, nor was Rodrigo's knockdown.

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Koscielny gets in the way of Moreno's shot 25 yards out. Arsenal looked positive for the first five minutes of the game, but since then they have had no rhythm to their play whatsoever. Their supporters are now starting to urge them on.

SAVE!  Parejo's shot from outside the box is parried by Cech. Maitland-Niles attempts to head it back to his keeper but does not get enough on the ball and Guedes hooks it over the crossbar with just Cech to beat. Arsenal are all over the place!

GOAL!  ARSENAL 1-1 VALENCIA (ALEXANDRE LACAZETTE)

Arsenal level up the match through their first real attacking move the evening! Ozil plays the ball to Lacazette, who slides it through for Aubameyang. The Gabonese striker unselfishly holds the ball up and, with Neto stranded, he returns the ball to Lacazette to convert into an empty net.

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Only Ian Wright (three) has scored more European semi-final goals for Arsenal than Lacazette (two, level with Steve Bould and Charlie George). The big man for the big occasions! These opening 20 minutes in North London have flown by.

Aubameyang wins the ball back for his side and he is allowed to carry it as far as the opposition box. The striker has every right to take on the shot but he can only scoop it over the crossbar, with Neto happy to watch it float over his head.

There have been two shots on target in the opening 25 minutes and two goals. There has not been a great deal between the sides so far and 1-1 is probably just about right. Arsenal are looking very vulnerable at the back, though, so Valencia will fancy their chances of scoring another away goal.

GOAL!  ARSENAL 2-1 VALENCIA (ALEXANDRE LACAZETTE)

Arsenal have turned the game on its head in the space of seven minutes! Xhaka's cross into the box is headed into the ground by Lacazette and Neto is unable to keep it out. The Valencia keeper pushes it away with both hands but he was well over the line at that point - goal-line technology was not needed to give that one.

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YELLOW CARD!  Lacazette makes contact with Xhaka's cross once again, but he cannot make clean contact with his attempt and it ends over the crossbar. The first yellow card of the contest is shown to Diakhaby for catching Lacazette in the chest with his high boot.

Arsenal have hardly been at full flow, yet they have managed to recover from a goal down to lead 2-1 here. Valencia do have an away goal, though, and Marcelino would probably take this scoreline if offered to him now.

CHANCE!  This is a big, big chance for Aubameyang to give Arsenal some breathing space. Xhaka picks out the Gabonese with another good delivery, but the volley from eight yards is sent into the ground and the ball bounces over the crossbar

This match is not too dissimilar to last season's semi-final first leg here, when Arsenal squandered some opportunities before being pegged back by Atletico Madrid. The Gunners' poor away form means they could really do with taking a 3-1 lead to Mestalla.

Parejo takes on the free kick from a long way out and cannot keep it on target. Valencia's best route through on goal is via set-pieces, but they have not really got the ball into the box since opening the scoring early on.

SAVE!  Maitland-Niles puts his pace to good use to get forward down the right and win a corner for his side. The set-piece is only half dealt with and Sokratis' audacious overhead attempt is on target, but Neto has a simple stop to make.

Arsenal are in control of the match for the first time as we enter the final stages of the first half. The Gunners lead 2-1 and they have looked a lot more stable over the last few minutes. Emery will be delighted with the response shown by his players.

Kolasinac bombs down the left after winning the ball back for his side but his final ball is once again lacking. The wing-backs overhits the cross and Aubameyang cannot make contact with it at the front post. Half time is now just a couple of minutes away.

The Gunners have dominated over the last 10 minutes. Valencia have gone back into defence mode, which was the case for the first five minutes of the match. Marcelino must decide whether to sit back on a 2-1 deficit or go in search of another goal in the second half.

HALF TIME:  ARSENAL 2-1 VALENCIA

Arsenal take a 2-1 lead into half time at the Emirates Stadium after recovering from an early goal behind. The hosts started poorly but they are in control with a quarter of the semi-final tie played thanks to Lacazette's double.

Arsenal's run to this stage of the competition has been built on their solid form at the Emirates Stadium, but they conceded for the first time in 461 minutes at home in Europe when Mouctar Diakhaby popped up with an early goal. Two minutes after Ezequiel Garay had somehow fired Rodrigo Moreno's pass over the bar from a couple of yards out, Arsenal's defensive deficiencies were again clear to see as Diakhaby outjumped three opponents to head home another Rodrigo knockdown.

The home side were all over the place in the first 15 minutes of the match, coming close to conceding another goal when Daniel Parejo's shot was parried by Petr Cech, before Goncalo Guedes looped the ball over the bar after Ainsley Maitland-Niles nodded it right into his path. Arsenal soon clicked into gear and scored through their first attempt of the match, with Alexandre Lacazette sliding the ball through for Pierre-Emerick Aubameyang and then converting into an empty net once his strike partner returned it to him inside the area.

Lacazette then nodded Granit Xhaka's cross into the ground and past Neto, who was positioned behind the line when slapping it away, to put the Gunners in front and move himself level with Ian Wright for the most European semi-final goals for the club. The home side took control of the match in the lead up to half time, creating another good opportunity that Aubameyang failed to take as his volley from Xhaka's latest dangerous cross bounced over the crossbar.

BENCH WATCH!

ARSENAL SUBS: Leno, Monreal, Torreira, Elneny, Mkhitaryan, Iwobi, Nketiah

VALENCIA SUBS: Domenech, Lato, Wass, Santi Mina, Ruben Sobrino, Torres, Gameiro

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KICKOFF:  Valencia, who tailed off in the first half after taking an early lead, get us back up and running at the Emirates Stadium. A huge 45 minutes awaits both sides!

If this match does finish 2-1, you have to wonder which manager will be the happier. One thing is for sure, it will keep the tie nice and open for the second leg in a week's time. The Gunners are just looking to find their groove once again.

Guedes is given far too much space to play in Rodrigo, whose delivery into the middle is cut out. Soler then has a shot from distance and does not get very far with his attempt. Valencia have started the second half on top, as they did the first.

This is better from Arsenal. Xhaka and Ozil pull the strings in the final third, but the latter takes a little too long to get the ball into the box. Once Lacazette is picked out there are too many players around him and he cannot control the ball.

Arsenal are starting to take control of the match again following their slow start to the second half. Valencia do not really want to take any unnecessary risks - they are happy enough with their away goal, as long as they do not concede a third.

This is a very promising moment for Valencia. The lively Rodrigo creates some space out on the left and spots the run of Guedes, who cannot quite get his head to the ball ahead of Koscielny. Arsenal give the ball away once again but Valencia's latest attack comes to little.

Lacazette spins in the box but he cannot quite work a shooting angle. Arsenal knock the ball around 40 yards from the opposition goal but the visitors have eight men behind the ball - it is not easy to find a way through. Valencia attempt to counter but Sokratis clears the ball for a throw.

ARSENAL SUB! Torreira, who many people were certain would start today, replaces Guendouzi with nearly an hour played. The timing of the sub suggests that this is a planned change from Emery.

Sokratis makes a brilliant sliding challenge to bail out Koscielny following an error from his central-defensive teammate. Arsenal have lost their way again over the last five minutes - they cannot afford to gift their opponents a second away goal.

The game has become very sloppy. Arsenal have played some nice football at times and they nearly get things right on this occasion, but Xhaka's cross is a little out of Aubameyang's reach and the striker cannot make the contact he wanted.

CHANCE!  Aubameyang crosses the ball into a perfect zone for Lacazette to guide home for his hat-trick. Roncaglia missed the cross but Lacazette got his body shape all wrong and could not divert his header on target from six yards out.

SAVE!  This could be a huge moment in the tie! A long-range shot falls into the path of an offside Aubameyang and it is teed up for Lacazette to shoot, but he cannot beat Neto from seven yards. The Frenchman had to lift it over the keeper from there!

CLOSE!  Just like that, it could so easily have been 2-2! Parejo sends a corner to the back post and Diakhaby gets to it ahead of Cech. Thankfully for the Arsenal keeper, Mustafi was positioned near enough on the line to block the attempt.

YELLOW CARD!  Parejo catches Lacazette with a flailing arm and is cautioned by the referee. Valencia make a double change, bringing on Wass and Gameiro for Guedes and Soler for the final 20 minutes. This tie remains finely poised.

Valencia appear to have changed shape following that double substitution. That is a wise decision from Marcelino as, despite that chance for Diakhaby five minutes ago, Los Che have been second best for a while now.

SAVE!  This is a very good save from Cech, who spreads himself to block Gameiro's shot from the substitute's first real touch of the ball. Gameiro did well to slot his teammate in. Valencia are starting to look very dangerous all of a sudden.

ARSENAL SUB! Wass's free-kick is sent into a dangerous area and Diakhaby gets to it unmarked, but he heads over and was flagged for offside anyway. Emery makes his second change of the game by replacing Ozil with Mkhitaryan.

Kolasinac gets in behind but Garay just about cuts the ball out. Aubameyang is then nearly played through but former Arsenal man Paulista gets a touch to the ball at full stretch to deny the current Arsenal star. Both sides are pressing for the fourth goal of the match.

Gabriel appeared to jar his knee and there was a stoppage in play for the ex-Arsenal man to receive some treatment, but he is OK to continue. We are now into the final 10 minutes and there is little between the sides.

SHOT!  Valencia squander another good opportunity. Wass gets in behind down the right and cuts the ball back for Gameiro, who juggles the ball and then blasts it over the crossbar when finally managing to get the shot away.

ARSENAL SUB! Monreal comes on for Koscielny, who has not been moving freely for a while. Emery has now made all three of his changes, while opposite number Marcelino still has one more sub available to make should he wish. Valencia are looking the more likely to score at the moment.

Mkhitaryan gets between two opposition players but cannot pick out a teammate from his cut-back right on the penalty spot, with Aubameyang charging into the six-yard box. I think both managers would probably take the full-time whistle now.

Lacazette closes down Neto and forces the goalkeeper into an error inside his own box. The Arsenal supporters loved that - the Frenchman has had a very good game.

The tempo of the match has dropped quite a bit. Emery would have liked a third goal but it does not look as though his side are going to find it.

GOAL!  ARSENAL 3-1 VALENCIA (PIERRE-EMERICK AUBAMEYANG)

What a massive goal this could be for Arsenal! Neto produces a superb save to deny Lacazette a hat-trick, but Kolasinac sends the loose ball into the six-yard box and Aubameyang is left in space to convert the volley past Neto at the back post. Poor defending!

Three of the four added-on minutes have been played and there is no doubt who will be the happier of the two sides now. That Aubameyang goal changes everything, setting Arsenal up nicely for next week's second leg. This has been a chance missed for Marcelino's men.

FULL TIME:  ARSENAL 3-1 VALENCIA

Arsenal recover from an early goal to beat Valencia 3-1 at the Emirates Stadium in the first leg of their Europa League semi-final. The Gunners trailed to a close-range header from Diakhaby 11 minutes in, but Lacazette scored twice before half time and Aubameyang added a late third to leave his side in control of the tie ahead of their trip to Spain in a week's time.

That concludes Sports Mole's live text coverage of events from North London. An on-the-whistle report can be found by clicking here, and be sure to join us again at the weekend as we bring you updates from selected games from La Liga and the Premier League. See you then!