Doom, gloom and speculation about Louis van Gaal's future was replaced by positivity last week, with wins against Shrewsbury, FC Midtjylland and Arsenal complemented by teenager Marcus Rashford's remarkable emergence.

It had looked like United would be brought down to earth with a bump against Quique Sanchez Flores' impressive Watford outfit, only for captain Mata's free-kick to secure United a 1-0 win.

The result moves Van Gaal's men level on points with fourth-placed Manchester City, who have a game in hand, on a night when things could have been so different had the visitors turned large patches of dominance into a goal.

Odion Ighalo came close on a number of occasions in the first half, with Sebastian Prodl threatening from set pieces as Watford continued to impress after the break.

However, they were struck by an 83rd-minute sucker punch as Mata directed home a left-footed free-kick in front of the Stretford End, extending United's winning run to four matches in all competitions.

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It was an unconvincing performance but one that had started reasonably for United, with Jose Holebas' mishit clearance in breezy conditions fortunate to find his goalkeeper, Heurelho Gomes, before the unmarked Anthony Martial headed wide at the far post.

Morgan Schneiderlin went closer still with an exceptional 20-yard volley, but by this point Watford were the better side.

Ighalo and Troy Deeney were threatening and the former should have done better when Daley Blind sent a shocking pass into his path.

Timothy Fosu-Mensah, making his first United start, then produced a fine, last-ditch challenge to deny the Nigerian striker, but his next challenge was far clumsier.

It led to a booking and free-kick from which Holebas and Prodl had half-chances, before Flores' men came agonisingly close as Deeney directed a header to Ighalo, whose spin and snapshot crept just wide.

The Watford striker continued to prove a nuisance and six minutes from the break surged down the right after United gave up possession, rode Fosu-Mensah's challenge and hit a low strike that David de Gea did well to stop.

The United goalkeeper saved his defence's blushes once again when Blind inexplicably left Guillermo Varela's pass back during a passage of play that saw the Dutchman catch Etienne Capoue with a lazy leg.

Penalty appeals were ignored and the visitors continued undeterred after half-time, with Ighalo closed out after Almen Abdi got in a cross.

Rashford's goal-line block prevented Prodl glancing in a corner as Flores' men upped the ante, with the confidence flowing through the side highlighted by Capoue's fizzing strike from distance just over.

United gradually got going as the match entered the final 30 minutes, with Mata stinging Gomes' palms before Rashford sent in a low ball that evaded a telling touch in the six-yard box.

Mata struck wide as United looked for a winner that they almost gifted the visitors.

Blind continued his poor evening at the heart of defence by ignoring De Gea's calls and sending a Holebas cross into Fosu-Mensah, but substitute Nordin Amrabat was unable to squeeze the ball home.

Ben Watson whipped in the resulting corner and Prodl showed great strength to meet it, powering his header just wide.

It was a missed chance they were made to rue after Miguel Britos brought down the returning Martial. Mata stepped up and produced a classy strike that beat Gomes and sent Old Trafford wild.