Chelsea 1 Barcelona 2: Special One faces biggest test after Barcelona storm Bridge

There have been so many days of reckoning in the career of Jose Mourinho and now, on 7 March, he faces another that competes with all the rest. All he has to do now is beat Barcelona on their home ground from a goal behind in spite of the extravagant talents of Ronaldinho and Lionel Messi. And last night the great Chelsea match-winning machine discovered just how impossible those forces can be to contain.

A red card for Asier Del Horno, an own goal from John Terry. It reads like the night that the football gods gave up on Mourinho but, in truth, this result reflected the balance of this match. The lingering question hangs over the dismissal of Del Horno, it was a decision that a thousand replays may never determine one way or another, but to listen Mourinho lampoon Messi's "theatrical" reaction, jarred a memory of Arjen Robben dropping to the turf at Anfield clutching his face.

The red card for Del Horno may have been harsh, but when it comes to condemning football's play-actors, Chelsea find themselves on very thin ice. To compete with Barcelona with 10 men was too tall an order even for the immaculately drilled players of Mourinho's squad, but they still went a goal up before succumbing to Samuel Eto'o's winner. At the Nou Camp they will attack, while Barcelona will protect their lead - it will be a thrilling exchange of roles.

Mourinho's first concern will be finding a left-back capable of stopping Messi and the fitness of William Gallas now becomes a primary concern for Chelsea. First Del Horno, and then Paulo Ferreira, were subjected to a humiliating ordeal by the running and dribbling of this formidable 18-year-old Argentinian talent. He was the game's outstanding player, and that was despite a Ronaldinho performance that grew in stature in the second half.

The sending-off took place in the 37th minute, interrupting a match in which the only shot had been from Ronaldinho - expertly saved by Petr Cech. A Chelsea strategy that prevented Barcelona shuffling possession out to Ronaldinho on the left had worked, though one of its consequences was that Frank Rijkaard's side increasingly relied upon the runs of Messi down the right as an outlet. He had already drawn one foul from Del Horno before they clashed decisively.

On 36 minutes, Messi broke clear of Robben and raced down the touchline towards the corner flag. It was, perhaps, the deftness with which heswerved round Robben's tackle that made Del Horno look so helplessly clumsy as the Argentinian came towards him. Whatever the reason, Del Horno's mid-air bodycheck of the teenager, with one foot raised towards him, looked dreadful.

It would have been a far worse tackle had Messi not realised it was coming, he turned his body away from the impact and, as they connected, the ball was nowhere near Del Horno's boot. The most generous assessment was that the £8m Spanish international had been caught out by the speed of his opponent, at worst it was a crude attempt to stop his opponent. The challenge was ridiculous, laughable even, but it lacked the edge of malice that so often accompanies straight red cards.

Messi went to ground while John Terry stood over Del Horno to protect him from the Barcelona players. Chelsea's left-back did his best to convince the Norwegian referee, Terje Hauge, that he, too, had been injured in the collision but that dreadful moment of impact must have been burned on the official's memory. He raised a red card to Del Horno without hesitation.

The first casualty of the Del Horno tackle was Messi, the second was Joe Cole, who looked bereft at being called to the bench to allow Geremi to take up the role of left-back while Ferreira switched flanks. It would take all Mourinho's great powers of improvisation to keep out a Barcelona team that were liberated by Chelsea's reduction to 10 men. For more than 70 minutes, they succeeded.

Although Mourinho had criticised Barcelona in his programme notes for their obsession with the Stamford Bridge pitch and their thirst for revenge, he placed an arm around Rijkaard's shoulders in the second half as the two men discussed the game. Mourinho had brought on Didier Drogba for Hernan Crespo at half-time, sensing, perhaps, that this was about to become a battle of strength and soon his side were rewarded when Eidur Gudjohnsen began a move in midfield, striking a ball out wide to Robben on the left who was brought down by Oleguer. Frank Lampard's low free-kick he whipped in from the left bounced in front of the goalkeeper Victor Valdes and was deflected past him by his own defender Thiago Motta.

It was a moment of joy for the Chelsea bench, but it was only the beginning of Mourinho's first-ever Stamford Bridge defeat. On the right, Ferreira could not contain the menace of Messi - and on the left, it was time for Ronaldinho to stir. With 71 minutes gone, the Brazilian's curling free-kick was deflected past Cech by the head of Terry.

It was a desperate blow for such a formidable player and then the siege began in earnest. Minutes later Terry kicked a shot from substitute Henrik Larsson off the line and Messi's shot struck the bar. On 80 minutes, Larsson cut the ball back to Rafa Marquez on the edge of the area and his cross was headed home by Eto'o at the back post. The tie remains Barcelona's to lose - or, more poignantly will take all of Mourinho's cunning to win.

Chelsea (4-1-4-1): Cech; Ferreira, Carvalho, Terry, Del Horno; Makelele; Cole (Geremi, 40), Gudjohnsen, Lampard, Robben ( Wright-Phillips, 78); Crespo (Drogba, h-t). Substitutes not used: Cudicini (gk), Maniche, Duff, , Huth.

Barcelona (4-3-3): Valdes; Oleguer, Puyol, Marquez, Van Bronckhorst (Sylvinho, 69); Deco (Iniesta, 85), Edmilson, Motta (Larsson, 66); Messi, Ronaldinho, Eto'o. Substitutes not used: Jorquera (gk), Belletti, Ezquerro, Van Bommel.

Referee: T Hauge (Norway).