Etienne Capoue's goal on the stroke of half-time was enough to send Watford into the quarter-finals of the FA Cup, beating QPR 1-0 on Friday.
As four minutes of added time were shown at the end of the first half, Capoue swept the ball home after a mis-hit from Tom Cleverley and it proved to be the winner.
QPR created plenty of chances but lacked a clinical finish after playing their fourth game in ten days, with captain Toni Leistner sending the ball wide from close range in the final few minutes.
Watford will now be in the draw for the FA Cup quarter-finals, which will take place after Chelsea vs Manchester United on Monday evening.
QPR: Lumley (6), Furlong (7), Leistner (6), Hall (6), Wszolek (7), Cousins (6), Luongo (6), Freeman (7), Bidwell (7), Wells (7), Smith (7).
Subs used: Hemed (4), Eze (5), Osayi-Samuel (n/a).
Watford: Gomes (7), Janmaat (7), Kabasele (7), Britos (8), Holebas (7), Hughes (6), Capoue (7), Cleverley (7), Sema (6), Deeney (5), Gray (5).
Subs used: Mariappa (5), Doucoure (5), Quina (n/a).
Man of the match: Miguel Britos.
It took a while for the game to get going, but Heurelho Gomes did make a few good collections after the 20-minute mark, first leaping to save a Pawel Wszolek cross before stretching to keep out a free kick from Luke Freeman.
Watford also went close not long after as Daryl Janmaat whipped an effort just past the post and it was a similar story at the end too as a cleared corner fell to the feet of Massimo Luongo, but his fierce strike also flew past the upright.
QPR ended the half strongly and had two brilliant chances to take the lead. The first was in the 37th minute as Michael Smith headed a Freeman cross just wide of the post - although he was flagged for offside. Four minutes later and Freeman latched onto a woeful midfield pass from Watford, burst down the field before chipping a ball over the top for Nahki Wells. He then struck with his first touch, forcing a fine save from Gomes as the ball went behind for a corner.
QPR named the same matchday 18 from their defeat to Bristol City on Tuesday. Watford made five changes with Heurelho Gomes, Christian Kabasele, Miguel Britos, Tom Cleverley and Andre Gray coming into the XI.
But QPR's wastefulness was punished by Watford on the stroke of half-time. Jose Holebas delivered an outswinging cross, which Cleverley mis-hit over on the right of the area. But the bobbling ball landed at the feet of Capoue, who hooked it back across goal and into the bottom corner.
QPR continued to see the better chances in the second half and went close inside two minutes with Freeman just sending a shot wide of the post. 15 minutes later, Wells latched onto a poor Christian Kabasele pass, drove towards goal but could only send his shot past the upright. Watford's best chance of the second half was in the 69th minute as a cleared corner landed to Cleverley, but his effort from range lifted over the crossbar.
The hosts should have equalised with three minutes of normal time to play. Freeman delivered another good free kick, which found Darnell Furlong at the back post. He fizzed the ball across the face of goal which Leistner came racing in to meet, but his touch sent the ball agonisingly wide of the post as Watford saw out their victory.
Queens Park Rangers have lost six of their last eight games in all competitions (W1 D1), after a run of six games unbeaten directly before that (W4 D2).
Watford have kept five clean sheets in their last six games in all competitions, as many shut-outs as they managed in their previous 24.
Watford have won eight of their last nine FA Cup ties against sides from a lower division, losing only against Millwall in the fourth round in 2016-17.
Etienne Capoue's winner came courtesy of Watford's only shot on target of the game
Man of the match - Miguel Britos
Miguel Britos does not get much game time these days, but he certainly gave manager Javi Gracia something to think about with his performance at Loftus Road. QPR were the better attacking side but aside from some poor finishing, Britos was certainly a big part of keeping them at bay.
He made a number of vital clearances and had QPR striker Smith marked well throughout, with the pair clashing heads early on as they went for the same ball. He continued to make superb blocks and clearances as Watford booked their place in the next round.
QPR are back in Sky Bet Championship action on Tuesday when they host West Brom, live on the Sky Sports Football red button. Watford travel to Cardiff in the Premier League on Friday.