Having secured promotion last week following a 2-0 victory at Brighton, and subsequent results involving Middlesbrough and Norwich City going their way, the Hornets knew they simply had to match or better what the Cherries achieved at Charlton Athletic to go up as champions.
One goal from Matej Vydra – his 16th of the season – looked to have been enough but Watford had several other fine opportunities to make what was a comfortable victory more reflective of their dominance against the Owls.
They were opportunities they were to regret not taking because although they were in complete control, they were to be undone when Atdhe Nuhiu headed home after the Hornets had failed to clear their lines from a late free-kick.
Slavisa Jokanovic’s side started positively and had an early appeal for a penalty turned down when Troy Deeney went to go round Chris Kirkland after latching onto Ben Watson’s through ball, but the Owls goalkeeper got just enough on the ball as the Hornets’ top scorer went down.
Kirkland denied the Hornets again in the 12th minute, blocking a Vydra snap-shot with his legs after Deeney had pressed the Owls defence into conceding possession.
The home side then had a period of controlling possession, while having to be patient, but in the 25th minute they made the crucial breakthrough to move back into pole position in the title race ahead of Bournemouth, who had opened up an early 2-0 lead at Charlton Athletic.
A mistake in the Owls defence let in Deeney and although he was again thwarted by Kirkland, Vydra followed up to head into the unguarded net.
The Hornets then sought to turn the screw as Ikechi Anya fired into the side netting, before Deeney set up a great chance for Almen Abdi but the Swiss midfielder placed his attempted finish wide of the far post.
The chances kept coming an Abdi had another superb opportunity shortly before half-time when Deeney and Marco Motta had combined to slice opening the Owls defence, but this time he shot over with only Kirkland to beat.
A fine challenge from Lewis Buxton deflected over a Deeney shot soon after the restart but although the Hornets continued to dominate, some of the impetus went out of their play.
Jokanovic brought on Juan Carlos Paredes, Daniel Tozser and Odion Igahlo to try and freshen things up. But evidence that it was perhaps not Abdi’s afternoon came with around 20 minutes to go when he was released by Deeney but a heavy first touch let the midfielder down when it mattered.
But Watford’s failure to score a second did not look like it would matter until late on when the Owls were awarded a free-kick, which was not dealt with and Nuhiu headed home from his side’s only chance on target.