Match ends, Manchester United 1, Watford 0.
Juan Mata's late free-kick earned Manchester United a win over Watford to move them level on points with fourth-placed Manchester City.
United striker Marcus Rashford was quiet in the first half as Watford's Odion Ighalo wasted two good chances.
But the hosts improved when Rashford switched places with Anthony Martial and the Frenchman won the free-kick which Mata curled in from 20 yards.
City have a game in hand on United, who earned a fourth successive win.
Had Ighalo not shot wide from Troy Deeney's flick-on or chose to pass to his strike partner when David de Gea thwarted the Nigerian, the story of the match may have been very different.
But buoyed by the recent form of Rashford and Mata scoring his eighth goal of the season, the prospect of United reaching next season's Champions League looks a distinct possibility after their city rivals lost 3-0 at Liverpool.
How did United's youngsters perform?
It was less than a fortnight ago that the future of United boss Louis van Gaal looked in doubt following an embarrassing defeat at FC Midtjylland in the Europa League.
Since then the gloom has lifted around Old Trafford with Rashford playing a telling part in previous wins over Arsenal on Sunday and FC Midtjylland the previous Thursday by scoring twice in each game.
Stationed up front for this encounter, he struggled to find time and space to drive at the well-drilled Watford defence, who were superb at blocking the hosts' efforts from distance.
Yet once Martial moved in from the wing, with Rashford replacing him there, the young Mancunian found the byline on several occasions and twice nearly created an opener.
It was because of the switch that Martial found himself positioned more centrally, drawing a foul from Miguel Britos as he bore down on goal, with Mata doing the rest.
Elsewhere, Tim Fosu-Mensah looked steady on his first United start in defence. He made several decent challenges and had a running battle with Deeney which he coped with well.
Was this another boring United win?
The hosts chalked up 11 successive goalless first halves at Old Trafford before the run ended on 2 February.
And although this game started the potential for another run to begin, Watford began faster in both halves and capitalised on some sloppy passing at the back from the hosts, which contributed to an absorbing match.
Only Watford's profligacy kept the scoreline goalless until Mata's late intervention and Deeney must have been fuming at Ighalo's attempts to end a run of only one league goal in 2016.
The defeat means that Watford are yet to register a win over top-five opposition this season, but they will rarely come as close as this as Ben Watson caused danger from several corners and Etienne Capoue, who had a decent penalty appeal, was excellent in midfield.
Perhaps their best chance came when Sebastian Prodl headed wide from two yards, under pressure from United defender Matteo Darmian.
The Hornets have now lost 10 successive games against United but with only three points needed to reach the magic 40-point mark, there is no danger of relegation and if Ighalo finds his range, they can push onto a lofty position in the league after promotion last season.
Man of the match - Etienne Capoue
Manchester United boss Louis van Gaal: "I have to give big compliments to our players because when it is physical and you can win at an important moment, when all our competitors are losing, it's very important.
"We lost against Sunderland and there was a lot of criticism but that is the strength of the league and now you see we are closer to the fourth position so now we are fighting for it."
On switching Rashford and Martial, he added: "That was a better change because Martial was not in the match and Rashford was not in the match and I changed them and they were both in the match. At that time we got the momentum."
Watford boss Quique Sanchez Flores: "We are a little bit disappointed, we try to be happy because the performance was amazing. We played with high personality and we tried to control the match. [United] played well in the last matches, so we prepared well but it was a special moment which decided the match.
"We are supporting Ighalo a lot because he is a little bit confused [with the fact he hasn't scored a lot recently], but he has had an amazing season."
Stats you need to know
- Manchester United named their fourth-youngest starting XI in Premier League history (23 years, 222 days old on average).
- Mata scored his first direct free-kick in the Premier League since December 2014 (versus Stoke).
- The Hornets have failed to score in six of their last eight Premier League matches.
- Odion Ighalo has scored just one goal in nine Premier League appearances so far in 2016, despite attempting 27 shots (inc. blocked).
- United won back-to-back Premier League games for the first time since 21 November 2015 - a day on which they also defeated Watford (away).
Manchester United are away at West Brom on Sunday before they travel to Anfield for the first leg of their Europa League tie the following Thursday. Watford can have their say in the title race as they host table-topping Leicester on Saturday.
- 1de Gea
- 51Fosu-MensahBooked at 23mins
- 5RojoSubstituted forDarmianat 70'minutes
- 21HerreraSubstituted forLingardat 77'minutes
- 8MataSubstituted forMcNairat 89'minutes
- 3BritosBooked at 82mins
- 22AbdiSubstituted forSuárezat 70'minutes
- 8BehramiSubstituted forAnyaat 86'minutes
- 24IghaloSubstituted forN Amrabatat 75'minutesBooked at 90mins
- 11N Amrabat
- Mike Jones
- Shots on Target
Second Half ends, Manchester United 1, Watford 0.
Corner, Manchester United. Conceded by Nyom.
Corner, Manchester United. Conceded by Miguel Britos.
Nordin Amrabat (Watford) is shown the yellow card for hand ball.
Hand ball by Nordin Amrabat (Watford).
Memphis Depay (Manchester United) wins a free kick in the defensive half.
Foul by Nyom (Watford).
Substitution, Manchester United. Patrick McNair replaces Juan Mata.
Offside, Manchester United. Marcus Rashford tries a through ball, but Memphis Depay is caught offside.
Corner, Manchester United. Conceded by Nyom.
Memphis Depay (Manchester United) wins a free kick in the attacking half.
Foul by Nyom (Watford).
Substitution, Watford. Ikechi Anya replaces Valon Behrami.
Goal! Manchester United 1, Watford 0. Juan Mata (Manchester United) from a free kick with a left footed shot to the top left corner.
Miguel Britos (Watford) is shown the yellow card for a bad foul.
Anthony Martial (Manchester United) wins a free kick in the attacking half.
Foul by Miguel Britos (Watford).
Corner, Watford. Conceded by Matteo Darmian.
Attempt missed. Sebastian Prödl (Watford) header from very close range is close, but misses to the right. Assisted by Ben Watson with a cross following a corner.