Marcus Rashford became the youngest scorer in the history of this derby in the Premier League as his winner gave Manchester United a victory that moved them to within one point of fourth-placed Manchester City.

Rashford showed his precocious skill at 18 years and 141 days with a demonstration of lightning pace and skill to skate past City defender Martin Demichelis before showing composure to slide a 16th-minute finish past keeper Joe Hart.

It was a calamitous day for City and manager Manuel Pellegrini. Not only did they slump to a loss that leaves them fighting off Sunday's opponents and West Ham for a top-four place, they had England goalkeeper Hart carried off early in the second half as he rescued his side from a desperate Demichelis back pass.

City, as well as England manager Roy Hodgson, will hope the injury is not serious, with captain Vincent Kompany already out for the foreseeable future after a recurrence of the Belgium defender's calf problem.

Raheem Sterling also went off injured early, a worry for City with a Champions League quarter-final against Paris St-Germain on the horizon.

Relive the Manchester derby here

Sergio Aguero headed against the post when City finally applied late pressure, while United should have had a first-half penalty when the panicking Demichelis stepped across Rashford as he closed in on goal.

In contrast, the under-pressure United boss Louis van Gaal greeted his celebrating players at the final whistle as their fans enjoyed a superb recovery from the Europa League elimination at the hands of Liverpool - and the revival of their Champions League aspirations.

Van Gaal's high-wire act

Van Gaal has been living with speculation about his future since before Christmas - and he awoke to more headlines before this game, with reports from Spain claiming an agreement was in place between United and ex-Chelsea boss Jose Mourinho.

And yet, once more, he managed to grind out an important win which not only gives United and their fans the pleasure of a victory over their arch-rivals but keeps them right in the hunt for a top-four finish.

Van Gaal has been criticised this season but one area where he deserves great credit is his willingness to have faith in young players - and Rashford delivered for him with a wonderful piece of skill and initiative that brought his goal.

He also made the wise decision to go without Marouane Fellaini against City. This meant United's temptation to play long balls towards the Belgium midfielder, awful in recent weeks, meant they could use the pace and width provided by Rashford and Anthony Martial.

It gave United extra fluency, as well as speed, without Fellaini clogging things up and slowing moves down - perhaps this will be a lesson Van Gaal will now learn.

The Dutchman may go at the end of the season - indeed the likelihood is that he will - but with United in the race for a Champions League place and still in the FA Cup, he may yet leave Old Trafford with something to remember him by.

Crumbling Man City?

When Manchester City announced that Pep Guardiola, perhaps the world's most coveted coach, would be replacing Manuel Pellegrini in the summer, the notion he would take over a club in the Europa League would not have crossed the minds of anyone at Etihad Stadium.

And yet, after this, City are now in a serious battle to stay in the top four - and to make matters worse their form is deserting them and injuries are starting to mount.

Kompany already faced another spell on the sidelines, while Sterling and, more crucially, keeper Hart also sustained injuries here.

City will be hoping Hart's injury is not too serious because they need all the help they can get behind a central defensive pairing of Demichelis and Eliaquim Mangala, who looked shot to pieces and an accident waiting to happen against the speed and mobility of Rashford and Martial.

They have now won only three out of 11 games since Guardiola's appointment was announced - and with rivals such as their Old Trafford neighbours and West Ham applying pressure, they need to rediscover their best form quickly.

Rashford for England?

The clamour will grow for the teenager after the flash of brilliance that led to the winner, accompanied by a selfless display of running that saw him take the ball into the corner to see the game out deep into the sixth minute of stoppage time.

Rashford's time will come but he also looked out on his feet, despite that late surge, after a run of eight successive starts.

He is undoubtedly a precocious talent but it may be too soon for Hodgson to be tempted into calling him up. One thing is certain - if it does not happen now it will happen before too long.

Man of the match: Marcus Rashford

What the managers said

Manchester City manager Manuel Pellegrini: "We did not deserve to lose. We dominated the game from the first minute and we were the only team who wanted to play during the whole game - but we missed three or four chance to score.

"We are still in fourth place and we missed clear chances to score. We have another 24 points to play for and every game is different. It was a mistake for our goal and I don't remember a lot of options for Manchester United other than that."

On a difficult match for defender Demichelis, who was substituted, he added: "Every player has bad days. Demichelis was nervous and it was not good for him to continue. We didn't score goals but that is not his fault."

Manchester United boss Louis Van Gaal: "I am a very proud manager.

"We played a very good first half with a goal and also had more chances and we didn't receive a lot of chances against us.

"This victory was necessary. The gap was four points and now it is one point, plus we are equal with West Ham, which is important. What is possible? I cannot say."

The stats you need to know

• The last time City failed to score in both games of a season against a single Premier League opponent was against Arsenal in 2010-11.
• Manchester United had just five shots including those blocked - their joint lowest number in a single league match this season (the other time against Crystal Palace in October).
• Meanwhile, Manchester City had 26 shots including those blocked - their highest number without scoring in a Premier League match since January 2012 (27 v Sunderland).
• Six of Manchester United's last seven Premier League away goals have been scored by English players.
• Manuel Pellegrini's City side have failed to score in three of their past four Premier League games.
• Louis van Gaal's United side have kept more clean sheets than any other Premier League side this season (14).

What next?

After the international break, Manchester City travel to Bournemouth for a 15:00 GMT Premier League fixture on Saturday, 2 April, while Manchester United host Everton the next day in a 16:00 GMT kick-off.