Barcelona beat Arsenal at The Emirates to take an important lead into the second leg, with Lionel Messi scoring twice.
The Gunners rarely threatened in the second half, despite bringing Theo Walcott on at half-time for the ineffective Alex Oxlade-Chamberlain.
Former Arsenal midfielder Emmanuel Frimpong was unimpressed with Arsenal's lack of conviction.
Arsenal always flatter to deceive— EMMANUEL FRIMPONG (@IAMFRIMPONG26) February 23, 2016
Arsenal had looked like they might keep Barcelona scoreless, but they were caught on the break in the 71st minute by a blistering counter attack from the La Liga side.
Luis Suarez and Neymar were both involved before Ballon d'Or winner Lionel Messi finished off the move, scoring his first goal against Petr Cech. Suarez hit the post minutes later as he came close to doubling Barcelona's lead.
They did so late on as substitute Mathieu Flamini gave away a penalty... with his very first touch, which Lionel Messi scored to make it 2-0, sending Petr Cech the wrong way.
Luis Suarez also missed an opportunity just before half-time as he headed wide from close ranger, but to go in 1-0 down at the break would have been harsh on Arsenal, as Barcelona did not have a shot on target during the opening 45 minutes.
The Gunners attacked from the off and defended well in the first half, arguably the better team, although were let down by sloppy play in the final third.