Monday night a heavy deflection earned Watford three points. Five days later and another one condemned them to defeat at Bramall Lane.

McBurnie will try and claim the goal but his header was going back across the six-yard box until it clipped Porteous on the shins, sending the ball spinning under Bachmann and past Choudhury on the line.

Small margins and yet it was also punishment for switching off at a corner, as McBurnie was able to peel off and get a header in unchallenged.

Until then Watford had looked solid at the back, although it’s fair to say the home side had enjoyed the lion’s share of the ball after the interval – the first 45 minutes were very even.

The Hornets didn’t muster a shot on target in the opening half, although they had justified appeals for a penalty when Davis appeared to be shoved as he was about to shoot in the 10th minute.

Before the home side went ahead Watford carved out a great chance but having earned himself a header in space, Pedro nodded Morris’s cross down but not at goal and it struck Davis before rolling harmlessly through to the keeper.

Watford have played far worse this season and there was no denying their effort and commitment. The home side didn’t overly trouble them but that one lapse in concentration from a set-piece was cruelly punished.

The main problem is for all their work they carved out very few chances. Possession in the opposition half has to result in something, and too often it didn't.

When it did the crosses were poor and the choices made were often not the best ones.

Now Watford are eighth and three points outside the play-off places. The next four games include three at Vicarage Road and they will have to make the most of that to ensure they don’t start finding the gap between them and the play-off places growing too wide.

Watford gave Louza his first start since he broke his ankle at Millwall in October. Kone dropped to the bench where he was joined by fit-again Cathcart.

After just three minutes Pedro hit a deep cross to the back post and Gaspar had time to have a touch, but volleyed it high and wide

In the 10th minute there were huge penalty appeals. Pedro slid Davis into the box and as he was about to shoot he was shoved sideways. Referee Mr Stroud was not at all interested, and the Watford bench were not happy

Seven minutes lager Sema drove a free kick from the left and Davis rose well to glance a header just wide.

In the 25th-minute the home side created their first real chance as Ndiaye ran at the Watford defence, got the benefit of a ricochet that gave him space to shoot, but then put his effort way over the bar.

The rest of the half was a lot of huff and puff without much end product and the first 45 minutes ended without an on-target goal attempt at either end.

Seven minutes after the restart Norwood curled a 25-yard free-kick but Bachmann got down to hold it.

Pedro then chipped a clever ball over the United defence, Sarr hooked a volley as it dropped but the effort was deflected wide

Fleck pulled the ball back outside the box in the 56th moinute and Ahmedhodzic side-footed a volley just over from 25 yards.

Watford should have dome better two minutes later. Morris crossed superbly from the left, Pedro met the ball unmarked but his header wasn't on target and bounced off Davis to Foderingham

United had the ball in the net in the 63rd minute but it was instantly disallowed as Bogle was offside when he headed home.

Two minutes later it needed a double save from Bachmann to maintain parity, first to push away Doyle's drive and then smother Osborn's follow-up effort.

However, in the 72nd minute United got the decisive goal and it was the first time Watford had made a mistake at the back.

McBurnie peeled off unmarked to meet a deep corner, and headed down. The ball deflected off Porteous and squeezed under Bachmann.

After that Watford probed without ever truly threatening to level, and the closest they came was right at the end of stoppage time when they sent Bachmann up for a late corner and there were two scrambles inside the box before the home side hacked clear and the final whistle went.

Watford: Bachmann; Gaspar, Porteous, Hoedt, Morris; Choudhury, Louza (Kone 57); Sarr, Pedro, Sema (Assombalonga 77); Davis (Araujo 80). Subs: Okoye, Cathcart, Bacuna, Kabasele