When Wayne Rooney scored the only goal of this first leg he burst towards a television cameraman near a corner flag and the crowd braced themselves for another moral panic. This time Rooney stopped halfway, dropped to the grass and rejoiced in silence. Fernando Torres would give anything just to have that choice.

Rooney, awaiting sentencing for his bark at Upton Park, has returned from the shadows to exert a major influence on two fronts, domestic and European. A hat-trick in the Premier League against West Ham was followed by this winner against Chelsea, for whom Torres was again an expensive passenger.

Just after the hour Carlo Ancelotti, the Chelsea manager, turned to his assistants to discuss the vexed question of which striker to take off: Didier Drogba, the iron horse of the club's most successful years, or Torres, a £50m expression of Roman Abramovich's power over team selection.

Few outside Abramovich's private box would have given Torres the nod to stay on. On came Nicolas Anelka and off went Drogba, laughing, shaking his head.

"I did it because Drogba played 90 minutes on Saturday," Ancelotti said, but no one was convinced by that. This was a season-shaping game and Torres was living off his price tag. These are the moments that tell you who really runs a club. As usual in Chelsea-United games, a refereeing error shaped the outcome. Patrice Evra's double leg-wrap on Ramires in added time ought to have led to a penalty. Long before then, though, Chelsea's latest quest to win club football's biggest prize had been warped by the splurge on Torres.

First, Chelsea deviated from their most effective shape, 4-3-3; then Torres was favoured over Drogba (and Anelka, in the first place), despite contributing little until his far-post header finally drew a save from United's Edwin van der Sar. Meanwhile Rooney was extending the personal gains of Upton Park, as if to stop us rattling on about his outburst or the months he spent as a spectre of his old self.

There are experts in the goalscoring arts who think the league's most expensive footballer has passed from El Niño to Old Man without stopping to enjoy the middle part. This was Torres's best chance yet to prove Abramovich has bought more than a newsreel film.

Torres had powerful supporters, among them Sir Alex Ferguson. "Of course he'll score again," the Manchester United manager said. "When Chelsea signed him, everyone was saying, 'What a great signing.' Now, because he hasn't scored yet, he's a bad signing. Ridiculous. Maybe he's just settling in from the Liverpool to the Chelsea system."

A statistical gem was that Torres and Drogba had shared 169 minutes on the pitch and exchanged precisely five passes. And one of those, apparently, was for a kick-off. With Chelsea's season in the balance the odd couple were squeezed together in the hope the fortune splashed on Torres would start to pay a dividend. His challenge, still, is to avoid being caricatured as the Andriy Shevchenko of the Ancelotti era: a striker past his best, bought on a proprietorial whim and rammed in to the starting team, irrespective of form.

As Ferguson insisted, it was too early for elegies. But there is good reason to worry. Torres has become a trudging player, flat-footed and slow to react, no longer the panther of his early Liverpool years. He has not scored in 12 games for club or country. A bright start faded into a muddle of miss-placed passes and doomed runs. A visible drop in confidence accompanied each error, which chimes with a theory popular in Spain. Torres spent so long wanting to get away from Liverpool that when the chance came a worm of self-doubt had burrowed into his brain.

That is enough of the sympathy. Chelsea have a season to save and only winning the Champions League can do it. Torres wanted in – wanted the money – and now he must deliver, or be hung in a gallery of men who peaked as boys and then saw it fall away. "He has to have confidence, keep going, he will score," Ancelotti said.

Another hard decision beckons for the return leg, where United will parade their away goal. With Rooney scuttling between midfield and attack here Chelsea's four were outnumbered by United's five, while Torres and Drogba worked in separate universes. As Drogba attacked Patrice Evra on the left, Torres tried his luck against Antonio Valencia, the second wide attacker to be redeployed at full-back by Ferguson in five days (Ryan Giggs was the first, against West Ham).

As the incompatibility of Torres and Drogba became apparent Ancelotti was obliged to weigh up the political implications of taking Torres off, as José Mourinho did with Shevchenko. Abramovich's power showed its hand. With 20 minutes left off came Yuri Zhirkov and Drogba and on went Florent Malouda and Anelka. The final indignity for Torres: a yellow card for diving. Even his acting backfires. There is a star player in there somewhere and Chelsea need it to report for duty at Old Trafford on Tuesday.