Match ends, Nottingham Forest 0, Watford 1.
Watford's top scorer Odion Ighalo came off the bench to fire the Premier League side into the FA Cup fifth round at the expense of Nottingham Forest.
The Nigeria striker, who came on in the 72nd minute, grabbed the winner with a minute remaining when he fired in from close range.
He now has 10 goals in his last 15 games, and 15 in total this season.
Watford also went close through new signing Nordin Amrabat, whose volley was saved by Dorus de Vries.
Watford showed little bite until Ighalo's second-half arrival, the 26-year-old brought on for regular strike partner Troy Deeney.
With a replay looming, Ighalo capitalised on Forest's failure to clear Allan Nyom's cross when he slotted home from inside the area.
Morocco winger Amrabat, who cost Watford over £6m, had earlier tested De Vries twice, while the keeper also made a good stop from Scotland international Ikechi Anya.
Forest manager Dougie Freedman will have been frustrated to see his side carve out just one effort on target, when Eric Lichaj's tame half-volley was easily held by debutant Costel Pantilimon.
The home side's best chance to score came moments before Ighalo struck, Dexter Blackstock picked out by Chris Cohen in the area but failing to get his shot on target.
What the managers said
Forest manager Dougie Freedman: "Overall I think we have contributed to a fantastic game today. In the first half we stood off a little bit too much - I think we paid them too much respect, although saying that we had the best chance of the game in the 45th minute.
"Second half we got at them and showed we could win this tie. We moved up a gear, had some exciting moments and created enough chances to win the game but half a chance and Watford have got the winner.
"Did they deserve it? No they didn't. But as long as I can see commitment in our performances we'll keep on marching forward."
Watford boss Quique Sanchez Flores: "Forest are a good team, but we controlled the match, had more possession and created more chances.
"Amrabat needs to know the system and the team-mates. He also needs to get used to the football in England.
"We were happy with the presence of Pantilimon and Amrabat today."
- 1de Vries
- 2LichajBooked at 90mins
- 37GrantSubstituted forOliveiraat 83'minutes
- 19WardBooked at 60minsSubstituted forOsbornat 68'minutes
- 21AnyaSubstituted forJuradoat 72'minutes
- 9DeeneySubstituted forIghaloat 72'minutes
- 11N AmrabatBooked at 82minsSubstituted forParedesat 86'minutes
- Neil Swarbrick
- Shots on Target
Second Half ends, Nottingham Forest 0, Watford 1.
Attempt saved. Ben Osborn (Nottingham Forest) left footed shot from outside the box is saved in the centre of the goal. Assisted by Nélson Oliveira.
Eric Lichaj (Nottingham Forest) is shown the yellow card for a bad foul.
Odion Ighalo (Watford) wins a free kick in the defensive half.
Foul by Eric Lichaj (Nottingham Forest).
Foul by Adlène Guédioura (Watford).
David Vaughan (Nottingham Forest) wins a free kick in the defensive half.
Corner, Nottingham Forest. Conceded by Nyom.
Goal! Nottingham Forest 0, Watford 1. Odion Ighalo (Watford) right footed shot from the centre of the box to the bottom left corner.
Attempt missed. Dexter Blackstock (Nottingham Forest) left footed shot from the centre of the box is close, but misses to the right. Assisted by Chris Cohen with a cross.
Substitution, Watford. Juan Carlos Paredes replaces Nordin Amrabat.
Hand ball by Adlène Guédioura (Watford).
Substitution, Nottingham Forest. Nélson Oliveira replaces Jorge Grant.
Nordin Amrabat (Watford) is shown the yellow card for hand ball.
Hand ball by Nordin Amrabat (Watford).
Attempt saved. Eric Lichaj (Nottingham Forest) right footed shot from outside the box is saved in the bottom right corner. Assisted by Dorus de Vries.
Foul by Nordin Amrabat (Watford).
Chris Cohen (Nottingham Forest) wins a free kick in the defensive half.
Corner, Nottingham Forest. Conceded by Ben Watson.