There was a frantic start to proceedings at Old Trafford as Athletic Bilbao, backed by an incredibly noisy set of travelling fans enjoyed the better of things. Manchester United struck first, but their opposition would eventually get the better of them as Bilbao defeated the Red Devils 3-2.
Moving the ball quickly and at will within the Manchester United half, you'd have been forgiven for thinking they were home side in this tie as Fernando Llorente and Iker Muniain posed all kinds of questions for Johnny Evans and Chris Smalling in the United defence.
It was Llorente who had the first real opening of the game after five minutes, when Wayne Rooney's sloppy pass was intercepted by the exciting Munain, he fed his fellow Spanish international and had he kept his balance the ball could well have been nestled in the back of David De Gea's net as opposed to a yard wide.
The visitors could also have felt aggrieved not to have a penalty awarded when Llorente had his shirt clearly pulled in the area by Chris Smalling, however it was United who would go on to open the scoring.
In all honesty, the home side had offered very little apart from Javier Hernandez tame effort straight at Iraizoz in the Bilbao goal early on, so it came as quite a surprise when Rooney gave them the lead in the 23rd minute.
Some neat interplay between Ryan Giggs and Park Ji-Sung set up Hernandez. The Mexican showed great composure to turn in the box and get the shot in which Iraizoz could only parry into the path of Rooney to blast in from close range.
Athletic didn't allow their heads to drop though, and had numerous chances to pull things level before Llorente eventually did. Markel Susaeta wasted a glorious opportunity when he skinned Evans for pace before sending a lob wide of the mark.
The equalizer came though. Iraola got forward well from right-back, laid it out wide to Susaeta rather than taking the strike on goal, and he sent in a great ball for Llorente to nod in powerfully from six yards out, giving Bilbao a share of the spoils at half-time, and a precious away goal.
The second half saw neither side hold back in attempt to take a lead into the second leg, and Athletic were out the blocks fast in a thrilling second half.
Muniain and Llorente were again the main protagonists, with Muniain being the first to test De Gea with a low drive from just outside the area, with the Spanish keeper's finger tips coming to the home side's rescue. United had De Gea to thank again moments later when he was at full stretch to deny Llorente ho'd sent a curling effort towards the top right hand corner.
The hosts however were not without their own chances in this end-to-end tussle, Rooney fired a freekick low towards the bottom corner was watched wide by Gorka Iraizoz, however the best of the Reds' chances fell to Hernandez, who found himself in the box with plenty of time, perhaps even too much time before he fired weakly at Iraizoz.
Then we had the breakthrough, and a game of stunning quality had a goal to match. Ander Herrera played an absolutely delicious dink over a static defence on the edge of the penalty area, and whilst United were caught napping, Oscar De Marcos lashed the ball left footed, low and across De Gea into the bottom corner. A truly magnificent goal.
Rooney jabbed and prodded at the Bilbao back line with shots of varying quality from varying differences, but it was Hernandez again who wasted a great opportunity to level things up. A great move started in United's own half by Rooney, followed by Michael Carrick's cross field ball to Nani, and eventually the ball landed with Hernandez, in the area, who dallied on the ball and the danger was eventually snuffed out, met by audible frustration by the home fans, and a certain Scouse striker who was very well placed and awaiting the ball.
Perhaps we were done, it had been an enthralling 90 minutes, and if nothing else happened we could all sit back and reflect on an exceptional display of football. Oh no, there was plenty left in the tank, and a controversial but correct call by referee Florian Meyer had a major hand in Athletic's third goal.
Patrice Evra will feel annoyed that a freekick was given against him for playing on with only one boot on, but technically it's within the rules of the game that it's a freekick. Athletic lumped it forward to Gaizka Toquero who didn't manage to get there, but De Marcos did, and smashed one towards the bottom corner. De Gea parried, Rafael seemed to fall asleep, and Iker Munain nipped in and popped the ball into the back of the net, getting a goal his performance richly deserved.
The drama wasn't over though, and in the first minute of stoppage time De Marcos' outstretched hand got in the way of the cross, and Rooney stepped up to send Iraizoz the wrong way, cutting the lead, and giving United a little more confidence headed into the second leg.
And what a second leg we have set-up at the San Mames next week. Sir Alex Ferguson said after the game that his side were beaten by the better team, and his side must do better if they are to progress in the tournament, and he's right on the money as whilst they had their moments, they were outplayed and outclassed for the majority of a thoroughly entertaining game.