Arsenal 0 – Barcelona 2: with just one leg played, this tie already looks over.
Football can be a cruel mistress sometimes; of the 3 recent ties Arsenal have played Barcelona in the Champions League in recent years, this was arguably the Gunners' best performance, and yet they come away with the worst result after the first leg.
Arsenal actually should have gone into the break 1-0 up, and gave as good as they got until Barcelona scored through Messi on the break.
Then Mathieu Flamini came on, and conceded a penalty within a minute, with what was essentially his first activity in the game (and he still didn't even touch the ball!)
But while that's a slapstick stat for Flamini, the Frenchman shouldn't be blamed too harshly: Per Mertesacker was badly at fault after horribly miscontrolling the ball.
Mertesacker is often pilloried for his lack of pace, but ironically it was his control who let him down in this instance.

Mertesacker living down to all my hype.
— Piers Morgan (@piersmorgan) February 23, 2016

Everyone blaming Flamini but do you understand how dead Mertesacker's clearance was. He's actually a dinosaur
— #BWIGM (@JamzLdn) February 23, 2016

So gutted. I think we've done really well. We have had some great chances and probably deserved to score… Then Flamini happened
— MGH (@OfficialMgh) February 23, 2016

If my son ever asks why I went to jail,
"KID, IT ALL STARTED WHEN FLAMINI GAVE AWAY THE PENALTY AGAINST BARCA "
— Ozilicious (@Goonerboy_49) February 23, 2016

Mathieu Flamini making an instant impact pic.twitter.com/4FvpLRrBD1
— Troll Football (@TrollFootball) February 23, 2016

Mertesacker trying to catch MSN there: https://t.co/JzCMBY4DM4
— Coral (@Coral) February 23, 2016

RAMSEY… MERTESACKER… FLAMINI pic.twitter.com/3AP4faJkTp
— Sith_God (@A_Young_Padawan) February 23, 2016

82' Mathieu Flamini subbed on
83' Mathieu Flamini concedes a penalty #UCL pic.twitter.com/iw7eCBRUn1
— ESPN FC (@ESPNFC) February 23, 2016

"Please have mercy on Mertesacker" pic.twitter.com/6QSYCnPKas
— ️ (@ffsDarmian) February 23, 2016

100 – Per Mertesacker's fastest time for the 100 metres is 2 hours and 44 minutes. Sluggish.
— OptaJoke (@OptaJoke) February 23, 2016