However, England rallied and Will Hughes put the win beyond doubt in the second half.
Read how all the action unfolded below:
4.32pmGood afternoon! It's just half an hour until kickoff at Stadion HNK Cibalia, where England Under-21s will be looking to book their place in next year's European Championship. Gareth Southgate has already named his side for the match, so let's take a look at the teams..
4.33pmENGLAND STARTING XI: Butland, Dier, Shaw, Hughes, Gibson, Moore, Berahino, Forster-Caskey, Kane, Carroll, Redmond
4.34pmENGLAND SUBSTITUTES: Garbutt, Bond, Lascelles, Ince, Woodrow, Pritchard, Baker
4.35pmCROATIA STARTING XI: Livakovic, Milic, Datkovic, Mitrovic, Bradaric, Pasalic, Milos, Halilovic, Pjaca, Rebic, Livaja
4.36pmCROATIA SUBSTITUTES: Delac, Galovic, Perica, Caktas, Bagaric, Brucic, Misic
4.38pmSo England have named an unchanged starting lineup for tonight's match. Saido Berahino will surely be the main dangerman for the visitors, having scored nine goals in nine appearances during this qualifying campaign. Meanwhile, Marko Livaja, who scored Croatia's goal on Friday, continues up front for the hosts.
4.41pmAs I mentioned in the introduction, Croatia's away goal could play a part this evening. As things stand, a single goal from the home side would send them through at the expense of England. However, should the Young Lions score first, Croatia will need at least two goals to keep their hopes alive.
4.44pmBerahino, who scored the winning goal in Friday's first leg, told reporters ahead of this match: "We are going to possibly encounter all sorts of situations and we have to be ready for anything. We expect Croatia to give their all and they won't give an inch at their place. It will be a time for cool heads. We can't go out there panicking. We have had a great campaign so far and we all look forward to every game that comes along."
4.46pmSpeaking of Berahino, here he is in training earlier:
4.49pmManager Gareth Southgate has also been speaking to the media ahead of kickoff. At his press conference, he said: "We controlled the game at home and we've got to have the ambition of doing that here as well. Obviously, Croatia will be lifted by their home support and they know they performed really well at our place so there's a bit of work to be done and I'm sure we're going to be tested in every department. But we feel confident that we can do the job."
4.52pmOne player to keep an eye on this evening will be Barcelona youngster Alen Halilovic. The 18-year-old featured for the senior side in their 6-0 win over Azerbaijan just yesterday.
4.55pmThe teams have just made their way out of the tunnel ready for kickoff. The national anthems for both sides will be played before the action gets underway.
4.58pmPREDICTION! With just a few moments until kickoff, there's just time for a quick prediction. Despite Croatia taking the lead on Friday, England really did look the stronger of the two sides, and scoring an away goal early would leave Croatia with a big mountain to climb. I think this will be 1-1 on the night, with England progressing 3-2 on aggregate.
1 minKICKOFF! Croatia get the match underway.
3 minCHANCE! Mario Pasalic collects the ball from a Marko Pjaca ball into the box, but Jack Butland makes a stunning save at full stretch to deny the Chelsea youngster. The home side win a corner as a result, but it's quickly cleared by the visitors. That was a dangerous moment for the visitors, who had been applying pressure down the other end themselves moments earlier.
6 minCHANCES! England go on the attack, with Berahino playing the ball in for Kane, but the Tottenham striker's finish from a tight angle is batted away by Livakovic in the Croatia goal. Kane returns the favour moments later, playing the ball in for his strike partner, but once again the keeper is ready.
7 minAfter a rather frantic opening five minutes or so, England try to settle the tempo of the match down, with Forster-Caskey and Hughes keeping the ball in midfield. The Derby midfielder tries a quick run to set up a chance for the visitors, and he wins a corner.
9 minGOAL! Croatia Under-21s 0-1 England Under-21s (Liam Moore)
9 minLiam Moore scores his first international goal, blasting the ball into the bottom of the net from a Tom Carroll corner. That's a huge goal for the Young Lions, as it leaves Croatia needing to score at least twice.
11 minCroatia try to push forward straight away as they look to get themselves back into this tie, but Pasalic's run comes to nothing when he puts too much on his delivery into the box, leaving Butland to gather it for the visitors.
15 minEngland have the ball back, and Luke Shaw tried to create something with a quick run down the left flank, but his cross in is swiftly dealt with by Mitrovic. Halilovic wins it back for the hosts and looks to catch England out on the counter, but the move fizzles out before Butland comes under pressure at the back.
18 minMoore's goal has really changed to atmosphere in the stadium. Prior to the goal, the sizable crowd had been fully behind the hosts, but they've been silenced by England's goal.
20 minA long ball forward falls to Eric Dier near the corner flag, and the defender has plenty of time to pick out Spurs teammate Harry Kane in the box, but the striker is penalised for a shove on Milos while turning to shoot, conceding the free kick.
23 minCHANCE! A poor clearance from Carroll almost gives the hosts a lifeline as he scuffs the ball into the path of Bradaric, but Pjaca's low strike is well saved by Butland.
25 minEngland respond well and immediately put Croatia to the test at the back again, with Redmond curling the ball in to Kane. The initial effort is blocked, before Berahino's effort on the rebound is cleared.
27 minRedmond is left feeling the effects of a rather clumsy challenge from Livaja after the Croatia midfielder tried to win the ball back near the edge of the England box. Redmond quickly shakes off the tackle though, while Butland comes forward to take the resulting free kick.
29 minEngland win another corner, having scored from their first. Livakovic makes sure that they do not add to the score this time around though, punching it clear before Carroll's delivery finds any of his teammates.
31 minMato Milos charges down the other end on the counter-attack for Croatia, but his efforts are for nothing as Alen Halilovic drifts offside while looking for a through-ball from his teammate. Antonio Milic makes a run a few moments later, but another offside, this time from Marko Livaja, costs the hosts this time around.
32 minCHANCE! Livaja creates some space on the edge of the box, and pulls it back for Pasalic, who arrives at pace, but his shot, taken first time, is easily saved by Butland.
34 minSUB! Croatia are making an early change, taking off Ante Rebic, and sending on Dalibor Bagaric. As far as I can tell, there was no injury for Rebic, so it must be a tactical change.
35 minThere could be a problem for England as well, as Will Hughes is moving somewhat gingerly. It looks like he's going to try and play on for now though.
37 minCHANCE! Berahino has the ball on the edge of the box, and despite there being plenty of defenders back for Croatia, he's given plenty of time to get the ball to Hughes, whose shot is blocked before Redmond sees the rebound saved.
38 minGOAL! Croatia Under-21s 1-1 England Under-21s (Marko Livaja)
38 minEngland are caught napping at the back, with Gibson and Moore both out of position as the ball is played in to Livaja. The scorer of Croatia's goal in the first leg has just Butland to beat, and he bests the keeper with a low strike into the bottom right corner. Game on!
41 minEngland are pushing to get their two-goal aggregate cushion back before the break, but Kane is unable to get on the end of a Redmond ball into the box, giving the hosts a goal kick.
43 minKane is on the charge again, with Carroll providing the cross for the striker this time, but he just slightly mis-times his run, drifting offside before the pass is made. England just look a little hurried as half time is approaching.
45 minThere's just a minute of stoppage time to be played. Croatia look to have one more attack before the half-time whistle, but Butland is on hand to collect Halilovic's ball into the box.
45+1 minHALF TIME: Croatia Under-21s 1(2)-1(3) England Under-21s
5.48pmSo with one goal a piece in the first half, England maintain their one-goal lead on aggregate over Croatia at the break in the second leg of their 2015 European Championship qualification playoff. Gareth Southgate's side are now just 45 minutes away from a spot in next summer's tournament if they can avoid conceding again in the second half.
5.52pmLet's take a look at some of the stats from the opening 45 minutes. England had the larger share of the possession with 57%. However, both sides had five shots, with only one off target for Croatia, while three tested the goalkeeper from England. Discipline has been a bit of a problem for the hosts though, as they've committed eight fouls to England's three. So far the referee has been lenient, not handing out any cards.
5.56pmAs things stand, England will be heading to the finals. However, another goal from Croatia would complicate matters. Should the score finish 3-3 on aggregate, there would need to be extra time and potentially penalties to split the sides. If England score again, that would tip the scales heavily in the favour of the Young Lions, as they would have two away goals to Croatia's one, meaning that a draw over the two legs would be enough for Southgate's side.
5.59pmThere are numerous other qualification playoffs taking place today. Italy have already booked their spot at the expense of Slovakia. Portugal appear to be heading through against the Netherlands, and there's a bit of an upset on the cards as Spain are losing 1-0 to Serbia.
6.01pmThe players are heading back out ready for the second half.
46 minKICKOFF! England get the second half underway.
48 minNeither side have made any changes at half time, although England did have their substitutes warming up during the break. Bagaric tries to set something up early on for the hosts, but loses the ball in midfield, while Berahino curls a shot well wide from the edge of the box.
50 minEngland win a free kick in a dangerous position. Carroll curls it in and it's flicked on by Shaw, but Datkovic is there to clear the danger for Croatia.
52 minAfter a fairly quiet start to the second half from both sides, England are piling forward as they look to add a second goal this evening. Hughes dodges a couple of tackles in midfield to get the ball to Berahino, who links up with Carroll before eventually getting a shot away, but it's blocked.
54 minCHANCE! Croatia are a couple of inches away from being back on level terms as Pasalic weaves through the England defenders to find Pjaca, but the midfielder's finish flies just high of the crossbar.
56 minBOOKING! Will Hughes picks up the first yellow card of the night for a heavy challenge on Mitrovic.
58 minCHANCE! Redmond does well to keep the ball alive after coming under pressure out wide. He hooks it in to Berahino, but his path is blocked. It eventually falls to Kane, but he rushes the shot and it goes high.
60 minOFF THE POST! England are really imposing themselves now with Berahino on the ball again. He launches a powerful effort from just inside the area, and has the keeper beaten, but his shot agonisingly brushes the outside of the post as it goes behind.
62 minEngland win two corners in quick succession as they continue to push for another goal, which at this stage would all but seal their place in the finals. The first is turned behind by Milic before Livakovic comes off his line to decisively punch the second well clear.
65 minMilic dashes down the left flank as he tries to create a chance for Croatia, who haven't seen much of the ball inside England's half since the restart. The left-back tries to cross it in, but Moore is ready and heads it away.
67 minCroatia are on the attack again, but it's Milic whose left to take the shot, and it ends up in the crowd, which is an impressive mis-hit as there's an athletics track between the edge of the pitch and the stand behind the goal!
68 minSUB! Croatia have made their second change of the night, bringing on Mijo Caktas for Mario Pasalic, who was busy in the first half but has seen little action after the break.
72 minGOAL! Croatia Under-21s 1-2 England Under-21s (Will Hughes)
72 minJust moments after Harry Kane had an effort saved, the Spurs striker set up Will Hughes from a shot from the centre of the box, and the Derby County midfielder timed it perfectly to pick out the bottom corner. Surely that will be enough for England now.
75 minEngland appear to be just trying to keep possession and run down the remaining 15 minutes as Moore and Butland pass the ball around at the back. Southgate is yet to make a change, so may look to send on some of his less-experienced players for the remaining spell.
78 minHughes and Berahino play the ball through midfield before Shaw crosses in towards Kane. Mitrovic gets to it first though and concedes the corner. But they'll have to wait as Croatia are making another change.
79 minSUB! Alen Halilovic, who was in action with the seniors last night, makes way for Misic.
81 minNathaniel Chalobah featured for the Under-21s earlier in the qualification campaign, and he seems delighted with the current scoreline:
Yes will what a finish lad. Almost there boys 👌👌👌— Nathaniel Chalobah (@chalobah) October 14, 2014
83 minCroatia have shown little attack since Will Hughes's goal, and a quick burst forward from Milos is easily stopped by Shaw. Meanwhile, the crowd, is starting to thin out as the home supporters realise this isn't going to be their night.
85 minCHANCE! England get forward again, but Harry Kane isn't able to curl the ball in from a tight angle.
85 minSUB! Southgate finally makes his first change, bringing on Thomas Ince for a late cameo in place of Nathan Redmond.
88 minMisic tries to get forward to create a late consolation goal for the home side. He manages to avoid a couple of tackles before picking out Livaja, but Moore is on hand to block the threat.
90 minThere are just two minutes of stoppage time to be played, before England can officially confirm their place in the 2015 European Championship.
90+1 minEngland win a corner as they look to finish in emphatic style. They take it short, but Carroll's backheel is quickly cleared.
90+2 minFULL TIME: Croatia Under-21s 1-2 (2-4) England Under-21s
6.50pmENGLAND UNDER-21S QUALIFY FOR THE 2015 EUROPEAN CHAMPIONSHIP
6.51pmSo goals from Liam Moore and Will Hughes give England a 2-1 win on the night and a 4-2 victory on aggregate, and seal the team's 10th win in a row, which is a new record for the Young Lions.
6.53pmThat's all from this match tonight, but stick around for coverage of the qualifiers for the Euro 2016 tournament, with Scotland, the Republic of Ireland and Germany all in action this evening. Thanks for joining me this evening, goodbye.