Match ends, Manchester United 2, Watford 1.
Ole Gunnar Solskjaer said Manchester United seemed "on holiday" as his reign as permanent manager began with a laboured win over Watford.
The victory was harsh on the visitors, who dominated possession for long periods and had superior chances, but it lifts United into fourth place above Arsenal, who play on Monday.
Marcus Rashford's 10th Premier League goal of the season, after a superb through ball from Luke Shaw, gave United a flattering lead.
And as Watford wasted further opportunities to earn their first league win at Old Trafford, Anthony Martial made them pay midway through the second half with a close-range finish.
Abdoulaye Doucoure scored a late goal to fray the home fans' nerves further.
"It was a really nervy last five minutes," said Solskjaer, who was appointed on a three-year-deal on Thursday.
"They made it difficult for us and it seemed as though we were still on holiday or the international break. Both teams feel they should have points.
"When I won trophies here, we didn't play well in every game but [today] we lacked zip, urgency, and fitness."
The victory ended a run of successive defeats for Solskjaer, and took United level on points with third-placed Tottenham, who travel to Liverpool on Sunday.
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United struggle as new Solskjaer era begins
After being appointed on Thursday, having lost only one of his 13 Premier League games in charge since taking over from Jose Mourinho in December, Solskjaer asked his side to work harder and warned against complacency.
However, there was a tiredness to their play throughout, which, but for Watford's wastefulness, would have been punished. Paul Pogba also lacked his usual influence.
Whether it was because of the international break or down to Solskjaer's new status, it was difficult to say. Far from being a party atmosphere inside Old Trafford as Ole continued 'at the wheel', there were times during the game when the wheels almost came off.
The visitors had 20 shots to United's eight, with eight of them on target, yet they were often tame. Doucoure could easily have given Watford the lead early on but fired wide from 10 yards.
Troy Deeney might also have had a case for a penalty when he was charged in the box by Phil Jones.
For all United's failings, though, Rashford's well-taken goal and Martial's bundled effort, which Watford thought was offside, helped grind out a much-needed victory to keep United's Champions League hopes on track.
Their goals, in addition to those previously from Romelu Lukaku and Pogba, also ensured United have four league goalscorers in double figures for the first time since the 1995-96 season.
Watford suffer from poor finishing
Watford boss Javi Gracia will be hugely encouraged by his team's performance, as they began both halves on top and showed they are good value for reaching the top 10 in the Premier League and an FA Cup semi-final.
Gerard Deulofeu, who had his black tights cut off early in the first half because they didn't match Watford's green away kit, was a constant threat on the left, while Deeney gave Jones and Chris Smalling a busy afternoon in defence.
Yet every time they fashioned a chance, they could not beat David de Gea or skewed off-target - until Doucoure's well-worked late consolation goal.
Not only did Watford miss out on a chance to win at Old Trafford for a first time, victory would also have meant they would have eclipsed their club Premier League record of 45 points, set in 2015-16.
But there were plenty of positives as Doucoure and Etienne Capoue bossed midfield, in addition to the threat down the flanks.
The only aspect the Hornets need to improve on before their FA Cup tie against Wolves on 7 April is their finishing.
'Frustration in the stands'
Analysis from Old Trafford by Simon Stone
There was a nod to Solskjaer's appointment as manager before kick-off with a brief blast of the Stone Roses' 'Waterfall' from which United fans have derived their 'Ole's at the wheel' song.
But in truth, there was not much different at Old Trafford today.
United fans have been singing Solskjaer songs since his appointment as caretaker boss in December and will probably continue to do so after the Norwegian leaves, whenever that is.
What Solskjaer's hero status will not do is shield him from the need to win football matches.
There were no complaints of him whatsoever but as the hosts laboured in the opening stages and gifted Watford possession on far too many occasions for comfort, there was frustration in the stands. And that became anxiety as Watford were presented with their chance to snatch a point in added time.
It's a fair bet that, by the time United next play here, against Barcelona in the Champions League on 10 April, the souvenir sellers will have got their act together and got themselves some Solskjaer manager-related material to sell.
But for this appointment to work in the long term, Solskjaer needs to build a winning United team. And for that to happen against better teams than Watford and in the long term, he is probably going to need new players in the summer.
Man of the match - Phil Jones
'It was the start of the rest of the season' - What they said
Manchester United manager Ole Gunnar Solskjaer: "It was the start of the rest of the season for us. If we can get 15 points, we'll be top three.
"Today will have done us the world of good fitness-wise. We know how hard it is to play against Wolves [United play them on Tuesday] so we need to make sure we have a team fit and available."
Watford boss Javi Gracia: "I think it was a very good performance, but a bad result. We didn't take the chances we created in the first half. We dominated the game, we had more possession, we created more chances. But we didn't score and they punished us.
"We are getting a lot of good results away but today was an exception. We need to improve before the next games.
"I'm a little bit frustrated. It was a good performance but we didn't take our chances in the beginning."
Manchester United travel to FA Cup semi-finalists Wolves on Tuesday (19:45 BST) before hosting Barcelona on 10 April in their Champions League quarter-final.
Watford face Fulham, who have lost all four games under caretaker boss Scott Parker, in the Premier League on Tuesday (19:45) before their FA Cup semi-final against Wolves the following Sunday.
The best stats
- Manchester United have won 11 of their 12 Premier League matches against Watford, losing the other in September 2016.
- This is the first time since the 1995-96 season (Scholes, Cole, Giggs, Cantona) that Man Utd have had four players score 10+ goals in a single Premier League campaign (Martial, Rashford, Lukaku, Pogba).
- Since his debut for Manchester United in February 2016, Marcus Rashford has scored 45 goals for the club in all competitions, more than any other player in that period.
- Man Utd goalkeeper David de Gea made seven saves in this match - only versus Spurs in August 2011 (9) and Liverpool in December 2014 (8) has he made more in a Premier League game at Old Trafford.
- Watford have lost each of their last 14 Premier League away games against 'big six' sides, since a 2-1 win against Arsenal in January 2017.
- 1de Gea
- 21HerreraSubstituted forPereiraat 63'minutesBooked at 90mins
- 8MataSubstituted forLingardat 63'minutes
- 11MartialSubstituted forRojoat 77'minutes
- 2JanmaatSubstituted forFemeníaat 55'minutes
- 11MasinaBooked at 82mins
- 19HughesBooked at 17minsSubstituted forSuccessat 81'minutes
- 7DeulofeuSubstituted forGrayat 73'minutes
- Stuart Attwell
- Shots on Target
Second Half ends, Manchester United 2, Watford 1.
Phil Jones (Manchester United) wins a free kick in the defensive half.
Foul by Miguel Britos (Watford).
Foul by Jesse Lingard (Manchester United).
Etienne Capoue (Watford) wins a free kick in the attacking half.
Andreas Pereira (Manchester United) is shown the yellow card.
Offside, Manchester United. Jesse Lingard tries a through ball, but Andreas Pereira is caught offside.
Jesse Lingard (Manchester United) wins a free kick on the left wing.
Foul by Isaac Success (Watford).
Goal! Manchester United 2, Watford 1. Abdoulaye Doucouré (Watford) right footed shot from the centre of the box to the bottom left corner. Assisted by Isaac Success.
Foul by Jesse Lingard (Manchester United).
Abdoulaye Doucouré (Watford) wins a free kick on the right wing.
Delay over. They are ready to continue.
Delay in match Luke Shaw (Manchester United) because of an injury.
Foul by Paul Pogba (Manchester United).
Isaac Success (Watford) wins a free kick on the right wing.
Foul by Paul Pogba (Manchester United).
Isaac Success (Watford) wins a free kick in the attacking half.
Offside, Manchester United. Marcos Rojo tries a through ball, but Marcus Rashford is caught offside.