As Watford’s players left the field at Old Trafford they must have wondered what might have been. They’d had chances. More than most have at Manchester United’s home. But none were taken. It proved costly.

For 82 minutes the Hornets caused the Red Devils numerous problems. David De Gea was excellent behind a shaky defence. And then came the sucker punch. Delivered by Juan Mata’s wand of a left foot.

The Spaniard’s influence in the game had grown during the second period. So when Anthony Martial earned the hosts a free-kick 20 yards out there was only one person who’d strike it.

Mata stepped up and curled the ball around the wall and past Heurelho Gomes. It was a sumptuous goal, although you sense Gomes will be disappointed to have been beaten on his side of the goal.

But that is what top teams can do. They have the quality required to change matches in an instant and leave opposing teams and their fans disappointed.

Going into the game Quique Sanchez Flores said changes to his side were likely. He kept his word.

In came Allan Nyom, Sebastian Prödl, Jose Holebas and Almen Abdi. Juan Carlos Paredes, Craig Cathcart, Nathan Ake and Nordin Amrabat dropped to the bench.

There was no sign of the Hornets being overawed at Old Trafford. They made a bright start, although defensively they looked a little shaky. Holebas almost turned a cross from Marcos Rojo into his own net and Martial headed wide at the back post.

United’s defence was makeshift and inexperienced and was constantly pressed by the Hornets. Chances were created. Inevitably they fell to Odion Ighalo.

The Nigerian first had a shot deflected wide before tamely shooting at De Gea from distance. On both occasions he had teammates in support but chose to go alone.

Ighalo came closer to breaking the deadlock in the 25th minute. Etienne Capoue swung a cross into the area, Deeney flicked on the ball and Ighalo, on the turn, directed a half volley just wide.

United’s attacking verve has seemed stunted throughout the season and against Watford’s organised defence, the hosts struggled to create chances.

Morgan Schneiderlin’s volley from distance which went narrowly past Gomes’ post was the closest Louis van Gaal’s side came before half time.

Watford’s best opportunity of the opening period came ten minutes before the break. Ighalo won possession and sprinted forward. He evaded the challenge of Tim Fonsu-Mensah and was one-on-one with De Gea.

Deeney was available to a pass. If the Hornets’ top scorer had squared the ball Deeney had a tap in. Instead he shot and De Gea saved, much to the frustration of the Watford skipper.

Moments later Ighalo was in again. Guillermo Varela under-hit a back pass and the Nigerian got to the ball before De Gea. He attempted to poke it around the Spaniard but he stopped the shot with his legs.

At half time Flores waited to greet De Gea by the tunnel. The duo seemingly have a father and son relationship. And despite the goalkeeper constantly denying his side, you suspect Flores offered kind words to his former player.

The pattern of the contest didn’t change in the second period. Watford continued to press United and chances came as a result.

Ighalo should’ve done better when picked out by Abdi in the box but hesitated and was tackled before Capoue thumped a strike narrowly over the crossbar at the start of the second period.

Prödl was then denied at the near post by De Gea and Ighalo again shot wide as the Hornets built momentum.

But all of Watford’s good work was almost undone on the hour. Holebas’ conceded possession in his own half and United pounced. The ball was worked to Mata whose rasping shot was pushed away by Gomes. It was a let off but it gave the hosts impetus.

The noise inside Old Trafford increased. For the first time Watford looked rattled. And Mata almost opened the scoring with an effort which curled wide.

Flores responded by introducing Mario Suarez in place of Abdi. Watford had four central midfielders on the field and it helped restrict United.

With 17 minutes remaining Flores made a bold call. Off went Ighalo and on in his place came Amrabat.

The forward almost made a decisive impact. A surging run from Holebas ended with a cross.

He was half cleared to Amrabat who poked the ball towards goal from four yards. But Daley Blind crucially got in the way.

A corner was awarded. Watson delivered and Prödl met the ball inside the six yard box. Everyone waited for the net to bulge but the defender headed wide.

It was a pivotal chance missed. From United’s next chance Martial powered forward and was halted by Britos. Old Trafford were expectant and Mata dispatched the free-kick expertly.

Watford attempted to mount a comeback but to no avail. They’d given plenty and had just come up short.

But there were several positives for Flores and his side to take despite the Hornets failing to score for the sixth time in league eight matches.

It’s Leicester City on Saturday next up for Watford. A chance for the Hornets to make a telling impact on the Premier League title race.

Manchester United: De Gea; Varela, Blind, Fosu-Mensah, Rojo (Darmian 70); Schneiderlin, Herrera (Lingard 77); Martial, Mata (McNair 89), Memphis; Rashford.

Manchester United substitutes: Romero, Riley, Rothwell, Weir.

Watford: Gomes; Nyom, Britos, Prödl, Holebas; Capoue, Watson, Behrami (Anya 85); Abdi (Suarez 70), Deeney; Ighalo (Amrabat 74).

Watford substitutes: Pantilimon, Cathcart, Paredes, Ake.