Manchester - Teenage sensation Marcus Rashford struck again as Manchester United won 1-0 at Manchester City on Sunday to rekindle their top-four challenge and fatally compromise their derby rivals' Premier League title hopes.
Rashford embarrassed hapless City defender Martin Demichelis to score the game's only goal in the 16th minute, taking his tally to five goals in eight first-team appearances and making him the youngest ever Manchester derby goalscorer at the age of 18 years and 141 days.
Victory took Louis van Gaal's side to within a point of fourth-place City, stemming a damaging run of four games without victory and creating hope that United may yet finish a testing season by claiming a Champions League berth.
City's grip on fourth place is also at threat from West Ham United and although they retain a game in hand on the teams above them, they now trail leaders Leicester City by a massive 15 points.
Compounding a miserable last derby for outgoing City manager Manuel Pellegrini, the hosts lost both goalkeeper Joe Hart and winger Raheem Sterling to injury.
With Vincent Kompany and Nicolas Otamendi having both succumbed to injury against Dynamo Kiev on Tuesday, it has been a week that Pellegrini may come to rue when his side cross paths with Paris Saint-Germain in the Champions League next month.
Buoyed by their historic Champions League success against Dynamo, City had attacked the game with purpose and twice went close to taking the lead through Jesus Navas in the early stages.
Fernandinho also headed over the bar from a Navas corner, but United's pace on the break gave them a ready outlet and in the 16th minute they struck.
Juan Mata fed Rashford on the edge of the box and the youngster planted Demichelis on his backside before tucking a shot past Hart to claim his own piece of derby history.
Shorn of captain Kompany and Otamendi, City were always likely to be vulnerable in central defence and Hart was called into action moments later to beat away a shot from Anthony Martial.
At the other end, Demichelis got his head to David Silva's free-kick, but the ball passed the wrong side of David de Gea's left-hand post.
An apparent groin injury to Sterling gave Pellegrini an opportunity to bolster his midfield, with Fernando entering in place of the England international and Yaya Toure moving forward.
It put Toure in a better position to inflict damage and he twice went close to equalising, curling narrowly wide with his left foot and then stabbing off-target after Bacary Sagna flicked on a Navas free-kick.
But Rashford had not finished his torment of Demichelis and in first-half stoppage time he went down in the box after the Argentine stepped across his path, only for referee Michael Oliver to dismiss his penalty appeal.
There was more to come for Demichelis after the break as an under-hit back-pass almost let Martial in, obliging Hart to make a rushed clearance.
In doing so, the England goalkeeper damaged his calf and had to be stretchered off, with League Cup final penalty shootout hero Willy Caballero taking his place.
Demichelis's nightmare was brought to an end shortly after when he was hooked in favour of Wilfried Bony, which saw Fernandinho drop into central defence.
City looked there for the taking and United poured forward in search of the reassurance a second goal would bring, Caballero parrying a deflected effort from Martial and Fernandinho blocking fortuitously from Rashford.
But the hosts survived to go in search of an equaliser, with Sergio Aguero lashing a shot wide and heading against the post from Toure's cross.
Still City came forward, but Toure was unable to pick out Bony after Aguero looped a header across goal and both Navas and Fernandinho sent efforts into the stand behind De Gea's goal.
Six minutes of injury brought one last sight of goal for Aguero, but after chesting down Silva's pass, he slammed wide.