Barnsley suffered a third straight Championship loss at the start of 2021 as they went down 1-0 at Watford on Tuesday evening.
The Hornets took the lead with a penalty midway through the first half after a handball by Callum Brittain.
The Reds competed well with their promotion-chasing hosts but lacked composure and quality in the final third.
They remain tenth, seven points off the play-offs and 14 clear of the relegation zone.
Valerien Ismael made only one change from the side that lost at home to Swansea City on Saturday evening as Romal Palmer came in for Herbie Kane in central midfield. Omar Ali, the 21-year-old centre-back, was on the bench for the first time.
The Reds played some good football in the first half but did not find the clinical final cross or pass to create chances, while their hosts were always dangerous on the break and could have been 3-0 ahead by half-time.
The visitors started brightly and a sliding Conor Chaplin was inches away from meeting a low Victor Adeboyejo cross from the right of the penalty area but he could not quite connect inside the six-yard box.
Chaplin's cross from the right midway through the second half was headed over by Cauley Woodrow ten yards out.
The hosts took the lead in the 27th minute from a penalty by Troy Deeney whose attempted cross had been blocked by the arm of Callum Brittain. Deeney smashed the ball centrally into the net via the hand of Jack Walton.
Palmer then shot well over the bar from 25 yards then Kiko Femenia smashed over from a similar distance after Andre Gray beat the the offside trap and rounded Walton before his cross into the box was missed by Mads Andersen but cleared by Michal Helik.
Watford should have made it 2-0 when Ken Sema brilliantly skipped past Chaplin and played Gray through on goal but he was denied by a good one-on-one save by Walton.
The hosts missed another huge chance two minutes before half-time when they broke from a Barnsley corner and Ismaila Sarr's low cross from the right wing was met by Gray deep in the box one-on-one with Walton but he dinked the ball over the bar.
Barnsley also began the second half well and, after some pinball in the home box following an Alex Mowatt free-kick, Callum Styles sliced wide from just inside the area.
Gray then put the ball in the net after Will Hughes' shot hit the post, but the flag was up for offside.
Ismael brought Carlton Morris and Dominik Frieser on for Chaplin and Adeboyejo before the hour-mark. Morris had a header saved from point-blank range by Daniel Bachmann but the referee had given a foul by Woodrow who won the initial header from the left-wing corner.
The hosts almost scored an own goal on 72 minutes when a sensational left-wing cross by the excellent Mowatt was headed towards his net by Francisco Sierralta but Bachmann leapt to his left to make a fine save.
William Troost-Ekong almost doubled the lead with Watford's first real chance of the second half as he made minimal contract with a right-wing cross by Femenia.
Barnsley thought they should have had a penalty deep in injury-time when Woodrow went down after contact from Craig Cathcart, but the referee waved the appeals away.
Watford (4-4-2): Bachmann; Femenia, Troost-Ekong (Cathcart 82mins), Sierralta, Masina; Sarr, Cleverley (Chalobah 71), Hughes, Sema (Zinckernagel 62); Deeney (Pedro 62), Gray (Ngakia 82). Goals: Deeney 27 (pen). Unused: Parkes, Wilmot, Navarro, Garner.
Barnsley (3-4-3): Walton; Sollbauer, Helik, Andersen; Brittain, Mowatt, Palmer (Kane 69mins), Styles (Sibbick 89); Chaplin (Frieser 57), Woodrow, Adeboyejo (Morris 57). Unused: Collins, Moon, Oduor, Schmidt, Omar. Yellow cards: Sollbauer.