Arsenal 2 Barcelona 1: It was a night to remember at the Emirates Stadium. First they had to cast off the spell that Barcelona weaved during the first half. Now all that is required of Arsene Wenger's team is to win at the Nou Camp in 20 days' time and they will have pulled off the most stupendous of comebacks.
If that sounds fanciful now, then you had to be in the Emirates midway through the first half when, to put it mildly, Arsenal were drowning amid that hypnotic wave of Barca passing.
A goal behind and light years off the pace it was impossible to imagine the game would end in a barrage of Arsenal counter-attacks and two wonderful goals.
But the reality is that Wenger's team go to Barcelona on March 8 with a fighting chance of eliminating the world's greatest passing team — let's be honest, the greatest team full stop — from the Champions League this season.
The goals from Robin van Persie and then substitute Andrei Arshavin changed everything. They might just change Arsenal's season. They have certainly changed the way we look at this team.
First Wenger's side beat Chelsea this season, now Barcelona. How they are growing up.
There is still much work to be done in the second leg but whatever happens in Catalonia, Wenger's team turned a corner last night. They have beaten Barcelona over 90 minutes, coming from one goal behind, and surely that means that anything is possible now.
There were many great performances in Arsenal shirts — Van Persie and Cesc Fabregas among them — but again and again the eye was drawn back to the brilliant Jack Wilshere.
If Barcelona resolved that this summer was to be the summer that they finally repatriated Fabregas perhaps they may now start thinking that really they ought to be taking Wilshere too.
There was a brief period at the start of the first half when the Barcelona passing machine was still yet to spark into life, when they were still getting their bearings and adapting to the surroundings.
Arsenal had a chance to score in those 10 minutes and they really should have taken it.
The folly of missing that half-chance, an opportunity carved open by Fabregas for Van Persie after the hard work had been done by Theo Walcott became evident as the game went on and the passing rhythms of Barca became more and more ominous.
By the midway point of the first half, the Spanish champions were utterly dominant.
By 26 minutes, they had scored one and should have had another.
By the end of the half, they should have had three in all and Wenger's players were starting to exchange desperate glances.
It was impressive, no arguments about that. Xavi, Andres Iniesta and David Villa had Arsenal running about chasing the ball in the manner you might expect of a humble Football League team visiting the Emirates on a daunting cup assignment.
There were periods when you thought Arsenal's presence on the pitch was little more than incidental. It became embarrassing at times for Alex Song, who was passed around.
Walcott, for all his effort in chasing back the full-back Maxwell, looked isolated, Samir Nasri too. The Arsenal defence was vulnerable.
Who from Arsenal emerged with the most credit from that first half? Wilshere was excellent especially given the unpromising circumstances. He was one of the few who won some tackles and his passing was expedient. He looked, not to put too fine a point on it, as if he belonged in a Barca shirt.
Lionel Messi missed a chance to put his side in the lead within 15 minutes when Villa divided the Arsenal defence and, running at goal, the Argentine chipped Wojciech Szczesny but missed the goal by an inch. That was the Barca way — mesmerise Arsenal with their passing and then slip a ball in between the home side's defenders.
Villa's goal was much the same. Messi ran at Arsenal, held off Song's weak attempt at a tackle, and put in Villa who struck his shot between the legs of the diving Szczesny.
Five minutes before the break, when Messi put the ball in the net but was ruled offside, there was a clear handball by Johan Djourou in the build-up which could have been a penalty, but Arsenal escaped.
By the hour mark the total of passes completed by Barcelona was 412. To put that in perspective Arsenal completed 203.
If there was a ray of hope for Arsenal come the return leg, it was the booking picked up by Gerard Pique that means he will be out of the next game. Carles Puyol is expected back from injury by then but it does at least mean Barca will not be able to revert to their first-choice central defensive pairing.
Van Persie's equaliser on 78 minutes came from Gael Clichy's ball into the left channel. The striker's decision to hit it inside Valdes' near post caught the keeper by surprise.
The winner was a classic Arsenal counter-attack. Fabregas released Nasri and he cut the ball back to Arshavin who hit a controlled shot past Valdes.
The tie had changed beyond recognition and Arsenal are in control.