1 Arsenal seemed mentally prepared for having to chase shadows
Arsène Wenger knew the key to the game would be not how well Arsenal played when they had the ball at their feet, but how well they coped without it. Arsenal usually enjoy a disproportionate amount of possession but last night the boot was firmly on the other foot, with Barcelona having the ball for long periods.
Arsenal however did not panic, but allowed their visitors to play keep ball, as long as the ball was kept as far away from their own penalty area as possible.
Of course Arsenal could not manage to keep the Barcelona virtuosos at bay forever, but when they lost possession they lined up with a virtual 4-5-1 formation and retained their formation well.
It will be the same again in the Nou Camp, where Arsenal's ability to stick to their formation and focus for the whole match will be tested even more closely. The advantage of Wenger's young team is they have the energy to run all day.
2 Barcelona fear the pace of Theo Walcott
Whenever Theo Walcott threatened the Barcelona back four, he had them running scared. Maxwell was drafted in at left back with Carles Puyol out injured, and never looked comfortable when Walcott took the opportunity to run at him. Puyol is likely to be fit for the return leg on 8 March but Gerard Pique picked up a yellow card last night and will be suspended – and Maxwell will have to deputise again.
Walcott was Arsenal's most threatening player, but his distribution at times let him down. However he is a far more clinical player this season, with 11 goals to his name, and if he gets a chance to score now he is much more likely to take it. Maxwell is not likely to be looking forward to meeting Walcott again.
3 Arsenal's defence responded superbly to the challenge
The heart of the Arsenal defence had been subject to a revolving door policy for the first half of the season, but since the start of last month there has been some stability, with Laurent Koscielny partnering Johan Djourou, in front of rookie goalkeeper Wojciech Szczesny. The trio all did well last night in the face of the best attacking team in the world, with Koscielny in particular outstanding.
More than once the Frenchman managed to nick the ball away and pinch possession when Barcelona looked threatening. Djourou also passed his own personal test against the free-scoring Barcelona front three, while behind the central pairing Szczesny was a calming presence in goal.
There was a danger the 20-year-old Pole might have been overawed by the occasion of facing Europe's best team on his Champions League debut, but he performed with distinction.
4 Jack Wilshere is right at home in this exalted company
Wilshere followed his impressive full England debut a week ago with another accomplished performance in the heart of the Arsenal midfield. He produced a couple of wonderfully sharp tackles to win possession, snapping at the heels of Andres Iniesta and Xavi to deny them space. He also showed his creative side with a couple of stunning passes, including one he hit wide to Cesc Fabregas that had Barcelona back on their heels.
Wilshere's growing understanding with Alex Song provides genuine protection in front of the back four, but it is his array of passing and comfort in possession that marks the 19-year-old out as a player of rare class.
5 Barcelona's goalkeeper is prone to errors
Robin van Persie's wonderful equaliser with 12 minutes to go, following David Villa's first-half goal, set up a wonderful finale, in which Andrei Arshavin fired home a glorious winner. But if Victor Valdes had kept out Van Persie's shot at his near post, as he really should have done, then Barcelona and not Arsenal would be going to the Nou Camp with the advantage. Valdes is a weak link in the Barcelona side, and his error sets up a wonderful second leg.