Myles Peart-Harris scored in the first half to put the Yellows ahead before a late strike from Mark Harris secured the three points.

Elsewhere, Portsmouth beat Middlesbrough and Leicester City lost to Swansea City, seeing Oxford rise to 22nd, still one point from safety.

For the first time in four games, Oxford got through the first ten minutes without conceding a goal as they fended off some early speculative crosses and a shot over from Imran Louza.

Jamie Cumming in between the sticks for Oxford United (Image: Oxford United)

A decent early move also saw Jamie Donley spoon a shot over.

Jeremy Petris looked like the Hornets’ biggest threat getting high up on the right but the U’s were looking promising on the break, winning a free kick on their right flank.

Cameron Brannagan’s ball in was not dealt with and fell to the feet of Peart-Harris who tapped home from close range for his second goal in yellow and blue.

The Hornets tried to hit back immediately, forcing a save from Cumming and seeing shots come in from Luca Kjerrumgaard and Nampalys Mendy.

Oxford United’s Ciaron Brown wrestles Watford’s Luca Kjerrumgaard for the ball (Image: Oxford United)

There looked a great chance for Donley soon after as Stan Mills found him on the break, the Northern Ireland international opting to shift onto his left instead of hit it first time, losing out to his marker.

Half time approached with Ed Still’s side looking unimaginative in attack, the U’s relatively comfortable, Michal Helik seeing the ball go wide from a free kick which the goalkeeper palmed against him.

An early second-half save saw Jamie Cumming tip Nestory Irankunda’s shot from range over the crossbar, before pressure from Oxford saw Brannagan have a shot blocked in the box.

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Further pressure saw Mills and Will Lankshear both head at goal, the former nodding over and the second at the keeper.

A few penalty appeals went unrewarded as Mills and Lankshear went over in the box as attempts followed from Donley and Mills from range.

Hornets substitute Mamadou Doumbia nodded wide before Yunus Konak swerved a shot at goal which was saved at the other end.

The Watford striker hit another shot over, Ciaron Brown then thwarting Irankunda in the box with a good tackle shortly after.

Nerves began to kick in as the game entered stoppage time, but they were quickly banished when substitute Harris latched onto the ball and drove into space before firing past Egil Selvik from angle to secure a massive three points.

Oxford: Cumming, Long, Helik, Brown, Spencer, Konak (Vaulks 90+3), Brannagan, Mills, Donley (Harris 87), Peart-Harris (ter Avest 78), Lankshear (Romeny 90+3)

Watford: Selvik, Petris (Keben 61), Pollock, Goglichidze (Ince 89), Abankwah, Mendy (Baah 60), Louza, Irankunda, Kayembe, Chakvetadze (Maamma 68), Kjerrumgaard (Doumbia 61)

Bookings: Peart-Harris; Irankunda, Louza

The right back has played in some huge matches recently, from big clashes in the Championship relegation battle to a World Cup play-off semi final against Italy with Northern Ireland.

Spencer grabbed his first goal for the club last time out against Portsmouth, scoring the U’s first in a 2-2 draw at Fratton Park.

“I think this has been probably one of the most important moments for me personally in professional football so far,” the Northern Ireland international declared.

Brodie Spencer first half (Image: Mike Allen)

“I’ve learnt, I’d say, more in this month than I have in my entire career so far, so it’s been really good to be fair for me. I’ve just been trying to take it all in and really just dial in and stay focused and not let the occasion get ahead of me.”

Oxford have gone from winning three on the bounce to drawing three of their last four games, experiencing highs and disappointing lows.

“It’s about keeping that level head, not getting too high on the highs and too low on the lows,” the 21-year-old continued.

“It’s about keeping level headed and I think we have a lot of experience in the group.

Northern Ireland’s Brodie Spencer (left) and Italy’s Matteo Politano battle for the b (Image: Mike Egerton/PA Wire)

“This sort of helps me and the rest of the younger lads keep that level head. There’s a lot of players in the team who have been in this situation before last season and they were able to fight out of it, so there’s no reason why we can’t go on and do it again.”

The Yellows face Watford this weekend, looking to win after going four without.

The Hornets triumphed 2-1 at Vicarage Road in the reverse fixture, Spencer starting the game under now-departed coach Gary Rowett.

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“[I am] very confident. I think every home game we’re confident, no matter who we play against. I feel like we’re sort of like a different kettle of fish when we play at home.

“The fans get behind us, they make it very loud. You want to do that every game, but I think that at the home game, it’s just about that bit extra special.

“When you’re in our position in the league, it’s the bare minimum: give 100 per cent. No matter how talented you are as a player, I think you can always go out and give 100 per cent and show a bit of fight, which is needed in this league.

“It’s important for us to keep stepping up and showing that fight in each game.”