Marcus Rashford was Manchester United's hero again as his goal secured a 1-0 win away to Manchester City in the Premier League on Sunday.
The teenager, who scored four times in his first two United appearances this season, struck in the first half to seal the derby spoils and reignite his side's hopes of a top-four finish.
City lost captain Vincent Kompany and Nicolas Otamendi to injury this week and suffered further blows when both Raheem Sterling and Joe Hart had to be taken off in what proved to be a frustrating game for the Etihad Stadium faithful.
Sergio Aguero hit the post with a header but clear-cut chances were few and far between as United defended diligently against a flat City attack, while attempting to use the pace of Anthony Martial on the break to stretch the home side.
Wilfried Bony almost turned in Yaya Toure's cutback and Jesus Navas fired narrowly over, but United held out for a first win at the Etihad since December 2012.
Louis van Gaal's side are now just a point behind fourth-placed City, who remain 15 behind league leaders Leicester City and are now almost certainly out of the title race.
Navas fired a half-volley narrowly wide after United failed to clear Sterling's cross, but chances were scarce in a cagey opening period.
David de Gea saved well with his legs when Navas drilled in a low shot after David Silva picked him out at the far post, but City were dealt a sucker punch as the visitors snatched the lead in the 16th minute.
Juan Mata fed Rashford, who skipped easily past the challenge of Martin Demichelis before slotting beneath Hart from close range.
Manuel Pellegrini was forced into an early change, with Sterling - who appeared to pick up a groin injury - replaced by Fernando, and matters could have been worse for City just before half-time had referee Michael Oliver chosen to penalise Demichelis when he bundled Rashford to ground inside the area.
City were struck by another blow when Hart, having stretched to beat Martial to Demichelis' poor backpass, had to be carried off with heavy strapping on his right leg within three minutes of the restart.
Replacement Willy Caballero did well to parry a Martial shot before Rashford just failed to convert Matteo Darmian's cross, as United looked to score a killer second.
Aguero had been quiet throughout but came within inches of an equaliser when he nodded Yaya Toure's cross onto the post, with De Gea beaten by the effort.
Another Aguero header went wide of the far post before Michael Carrick just managed to poke the ball away from Bony after Toure's pass, as City began to turn up the heat on Van Gaal's side in the closing stages.
But the visitors saw out the final 10 minutes with the backing of a vociferous away following to collect a potentially pivotal three points in their Premier League season.