Jimmy-Jay Morgan's first-half tap-in condemned Watford to back-to-back away defeats at West Brom on Saturday.
The Hornets had their moments at The Hawthorns but once again paid for missed opportunities at one end and vulnerability at the other.
The afternoon could have been very different had Othmane Maamma taken a big early chance, but his tame effort was saved, before the Baggies scored their winner just after the half-hour mark.
Harry Whitwell burst beyond the Watford backline and squared for Morgan to roll in the only goal of the game - and despite a spirited second half, they were unable to find a way through.
It leaves Alessio Dionisi's side without a win in four league games and means they have won just eight of their last 53 on the road in the league overall.
Watford made a very positive start to the game, Martin Payero at the heart of the action as he teed up a huge chance after just three minutes.
Maamma latched onto his pass and cut inside to shoot from close range, but his weak effort was straight at the keeper when a finish a yard either side would likely have made it 1-0.
Shortly afterwards, the Baggies had a big opportunity of their own, Morgan forcing a big save out of Federico Ravaglia after he'd bullied the Watford backline.
Dionisi's side posed some threat on the break but the Baggies grew in dominance, nearly scoring a freak goal when Kevin Keben's clearance 25 yards out from his own goal was closed down and Ravaglia dived to save.
The Hornets were struggling to pose any kind of attacking threat, Jordan Zemura shanking a cross behind from a rare foray forward, but did at least put a halt to the hosts' momentum as the clock ticked up towards 30 minutes.
Maamma and Bravo burst into the box to win corners but disappointing deliveries let Watford down, before Morgan had the ball in the net at the other end but had clearly fouled Ravaglia and was booked for his challenge.
Moments later, though, Morgan put it right.
Isaac Price beat Albert Eames down the right and fed Harry Whitwell to burst into the box and square for Morgan to tap in, Watford looking so vulnerable defensively again.
Zemura's 25-yard free-kick straight into the wall was the sum of their remaining efforts as they went in a goal down at the break.
They could well have equalised in the 10 minutes after the break, though, first when Luca Kjerrumgaard teed up Maamma for a blocked effort, and then Bravo for a shot from point-blank range that a defender also got himself in the way of.
Moments later, Maamma nodded down for Payero in the box, but the Argentine scooped his shot over the top as Watford threatened with more regularity.
The Hornets had certainly stepped things up, even with Keben and Edo Kayembe operating as makeshift full-backs after the withdrawal of Eames and Zemura.
Bravo was the next to threaten, heading Keben's cross straight at O'Leary.
On 70 minutes, though, the Baggies could easily have doubled their lead and Watford had Ravaglia to thank for making another top save to deny Aune Heggebo, who was through on goal.
Watford had most of the ball from there but just couldn't find a way through, West Brom happy to sit back and settle for their one-goal lead.
Debutant Stephy Mavididi had one of the better chances, twisting and turning inside the box but firing over with his left foot.
The Hornets continued to push but didn't create another clear chance, and late handbags soured the closing stages as Bravo was booked.
To make matters worse, Edoardo Bove received treatment on full-time and looked in distress as he held his knee.
Watford XI: Ravaglia; Eames (Coulibaly 59), Pollock, Keben, Zemura (Kayembe 46); Bove, Kyprianou, Payero (Nabizada 67); Maamma (Nabizada 67), Kjerrumgaard (Doumbia 82), Bravo
Subs: Bachmann, Walker, Clarridge, Vata
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