Kyriakos Papadopoulos's first-half header was enough to give the Germans a slender, but deserved 1-0 half-time lead in their second game in Group E.
However, Sergi Roberto tapped home a hard-earned equaliser on 80 minutes, before Luis Suarez curled home the second moments later to add insult to injury for Leverkusen.
Relive the drama with our live commentary below.
6.47pmGood evening ladies and gentlemen and welcome to our live coverage of Matchday two of the Champions League. Tonight, we're focusing on Group E and, specifically, Barcelona's visit of Bayer Leverkusen as the Catalans and holders hunt a first win, having been held to a 1-1 draw at Roma last time out. Bayer, who lead the group, thumped BATE Borisov 4-1 at the BayArena. Barca are the champions and all, but victory here isn't a foregone conclusion.
6.49pmBefore we have a quick check on the team news, let's examine how both sides have fared in the early stages of their domestic campaigns.
6.52pmSo, Barcelona, who also won the Primera Division last term, sit second after what has been an up and down start to the season. They won their first four games with relative ease, but a 4-1 defeat at Celta Vigo last week brought them back down to earth with a thud. It was an-off day to say the least. Their defence was, in truth, abysmal that day. Utterly abysmal.
6.54pmThey did, however, bounce back with a 2-1 win over Las Palmas, courtesy of a Luis Suarez brace, but Barcelona could have been forgiven for feel like they lost. It was a night which saw Lionel Messi limp off after just 10 minutes, with the Argentine now expected to miss up to six weeks with knee ligament damage! It's not ideal, is it?
6.57pmOn to Leverkusen now and Roger Schmidt's side appear to have rode out a stormy opening few weeks to the Bundesliga season. Bayer won their first two, but a three-match losing streak followed as they went down to Bayern Munich, Borussia Dortmund and minnows Darmstadt 98! However, they beat Mainz 05 1-0 six days ago, before smashing Werder Bremen 3-0 at the weekend and they'll hope to make it three wins on the spin tonight. Given how unpredictable they are, it's ever so hard to back against them.
7.07pmRight, let's start with the hosts and it looks like four changes by Enrique. Dani Alves and Jeremy Mathieu return at full back to displace Marc Bartra and Adriano. Further forward, Andres Iniesta comes back into the field to replace Sergi Roberto, while main man Messi is replaced by Sandro. Neymar and Suarez continue up front as usual.
7.10pmLet's look at ze Germans now and Mr Schmidt also names four changes from the 3-0 win at Bremen. Firstly, left-back Wendell returns, as do Hakan Calhanoglu and Kevin Kampl, who start in midfield. Who they will they be supplying? Why it's only Javier Hernandez, who replaces Stefan Kiessling as Leverkusen's spearhead tonight. Expect Wendell to give fellow Brazilian Alves a torrid time. He's a serious talent.
7.14pmIncidentally, if you want to have a quick read of our preview for this one then click here!
7.18pmHere's the man we'll all be looking at tonight as he bids to replace Messi. Good luck to him.
7.22pmPREDICTION! Let's get a pre-match prediction wrong and, despite Messi's absence, it's hard to look past the champs tonight. That being said, they really must ensure that their defence is tight because they were attrocious at Celta Vigo last week - and Bayer are better than Celta. They've got some diamonds here and they'll all be looking to enhance their respective reputations. 3-2 Barca.
7.25pmThis person isn't letting their love for Barcelona get in the way of a prediction. Or are they? Who knows.
7.40pmHere's your five-minute warning, folks! Excited? Me too. I think we've got a cracker on our hands.
7.43pmKevin Friend is one of those officials with the cattle prods tonight! Oh how the mighty have fallen. Martin Atkinson is the man in charge.
1 minKICKOFF: And we're off at Camp Nou. What a clash we could have on our hand. Barcelona get us underway.
3 minBarcelona fans are booing poor Atkinson already after the Englishman failed to award Rakitic a free kick after being fouled by Bender I think. High tempo game already.
6 minCHANCE! First real chance and it falls to Rakitic, who connects with Neymar's lofted cross but he can't direct his header past Leno. Big chance that and one that could come back to haunt the hosts because Leverkusen have started well.
10 minSAVE! Barca slowly but surely growing in control and Sando forces Leno into a very decent save now.
12 minCHANCE! This has to go down as a chance as Bellarabi pulls away from Pique at the crucial moment to reach Donati's pull back, but his swivel and volley is well over the bar. Should've done better.
15 minBarcelona are toying with Leverkusen, who are going to have to do a lot of running tonight. They've had their moments, as have Barcelona, but the longer it goes without scoring then the harder it'll be for the visitors.
17 minThis is a brilliant run by Hernandez as he shrugs off Mathieu to reach the byline, a matter of feet from goal, but his pull back is to the invisible man and Barcelona ultimately clear.
19 minCLOSE! Oh my word this is so, so close. It's Kevin Kampl, who cuts inside Mascherano and looks to bend it around Ter Stegen with his left foot and it's oh so close, but just misses the far post.
22 minGOAL! Barcelona 0-1 Bayer Leverkusen (Papadopoulos)
23 minSorry but this is one of the best deliveries you'll see, and it's from Calhanoglu as you might expect. He swings in the perfect corner, which is almost right underneath Ter Stegen's crossbar, and Papadopoulos simply nods it home from close range. Big question marks over Jeremy Mathieu, who didn't even contest the ball!
25 minDonati goes down injured and the Barcelona fans are furious. They think he's acting the cod, and he is because he's up again minutes later. Cheeky divil.
27 minSuch a bad ball from Hernandez here. He breaks on the counter, with Calhanoglu totally free to his right-hand side, but the Mexican fails to pick him out with a shocking ball. There's more goals in this for Leverkusen.
30 minHalf-an-hour in and Barcelona definitely know they're in a game. Actually, Bayer are beating Barca at their own high-intensity pressing so far.
33 minSHOT! Bellarabi, who's been excellent so far, bursts through Barcelona's midfield before drilling at goal fromsome 35 yards and, naturally, it's well wide. Barcelona have been rattled.
36 minIt would be easy to forgive Leverkusen for sitting back but they have absolutely no intention on protecting this lead so far. They're going for all three points and, as it stands, that look a very possible scenario.
38 minBOOKING:Well done Mr Atkinson, who books Neymar for diving and he's spot-on. Desperate times call for desperate measures.
40 minOFF THE LINE! Oh my word how has this stayed out? Neymar's effort comes back off the post and Sandro looks poised to smash home, but it's Papadopoulos who throws himself in front of the effort and it loops up and over the bar. Top class.
42 minSAVE! Good save by Leno as he denies Rakitic's free kick. It's a good spell by Barcelona this, but will they score before the break?
8.34pmWow. Did we see this coming? Well, yep, we said it. Barcelona have been out of sorts without Messi and Bayer Leverkusen have taken full advantage of that, with Papadopoulos heading them into a 22nd-minute lead. They've been the better side overall, good value for their half-time lead and, with no Messi to bail them out, it remains to be seen whether or not they can come back. Wow.
45 minWe're back and what a big test Barcelona have now. Can they come back, bearing in mind Messi is not here to bail them out? Time will tell.
48 minCHANCE! Oh my word it could and definitely should be 2-0, but Hernandez fluffs a glorious chance. New half but same problems for Barcelona and Hernandez.
52 minCHANCE! Sandro, if we didn't already know, is no Lionel Messi. He has a great chance but he drills wide of Leno's goal. We can't excuse that. That's three golden chances.
55 minSUB: Leverkusen make their first sub as Kiessling replaces the woeful Hernandez, who is booed off but only because of his Real Madrid roots.
57 minCLOSE! Much better from Barcelona as Neymar, on the half turn, flashes just wide and Enrique is having kittens.
60 minSUB: Left-back Jordi Alba comes on for the injured Iniesta, which is another blow on a night when nothing is going right for them. Bless.
63 minSUB: Another sub as Sandro is brought off for Munir. Is he the answer? I'm not so sure. Barcelona's lack of depth is being a little exposed tonight.
64 minYELLOW CARD: Calhanoglu goes into the book for a cynical handball. Barcelona about 30 yards from goal. Neymar stepping up...
65 minCLOSE! Not far away at all as Neymar curls just wide. Leno was nowhere near getting that.
67 minSUB: Bellarabi, probably the best player on the field, comes off for Julian Brandt. I'm surprised by that, but maybe he's carrying a knock of some description.
70 minCHANCE! Should be 1-1 as Pique heads straight at Leno. Either side of him and it's a goal. Barcelona just turning the screw now somewhat.
74 minRight, we've got, like, 16 minutes left and Leverkusen holding their own. Barcelona are getting closer and you can never write them off. What a result this would be.
76 minBOOKING: Alba, who's only been on the field for about 10 minutes, goes into the book for a little petulant kick-out at Jonathan Tah.
78 minRoger Schmidt still looks as cool and calm as ever, to his credit. He's 12 minutes away from masterminding a major scalp but he's unflinching.
80 minGOAL! Barcelona 1-1 Bayer Leverkusen (Sergi Roberto)
81 minIt was coming for the last 15 minutes or so, folks, and Barcelona finally level when second-half sub Sergi Roberto taps home from close range after Suarez's effort wasn't held by Leno.
83 minGOAL! Barcelona 2-1 Bayer Leverkusen(Luis Suarez)
84 minHeartbreak for Leverkusen, who are suddenly trailing 2-1! We said this would be a cracker and it's every inch of that. It's excellent from Munir, who skips by Wendell before laying off to Suarez, who curls beyond Leno from the edge of the box. It's a brilliant finish.
87 minCHANCE! Probably should be game over as the excellent Munir scuffs his chip wide of Leno's goal.
9.39pmWell, that's quite cruel for Leverkusen, who concede twice in the final 10 minutes to lose 2-1! They were the better team for large spells, but Schmidt's substitutions were a little suspect. Goals from Sergi and Suarez did the damage, after Papadopoulos's opener, and that's it! Thanks for tuning in and we'll see you next time.