Sema had given Watford a first-half lead, firing high into the net from close range after Darnell Furlong had blocked an initial effort from Keinan Davis.

A double substitution at the break paid off for the Baggies, with left-back Conor Townsend popping up in the box at a corner to acrobatically hook in past Daniel Bachmann.

Watford winger Ismaila Sarr - who scored from inside his own half in the 1-1 draw at The Hawthorns in August - looked to have made the decisive contribution with a fine first-time finish into the corner, only for the Hornets to surrender that lead when Jed Wallace capitalised on Bachmann's poor pass out to equalise.

However, ex-Albion boss Slaven Bilic was able to celebrate a victory against his former club when Sema cut in from the right and his shot from the edge of the box flew in off defender Pieters.

Both goalkeepers made smart saves during the flurry of second-half goals, while Sema also had an effort ruled out for offside shortly after Wallace had made it 2-2.

Watford ended their five-game winless run to go fifth in the table ahead of a trip to second-placed Sheffield United on Saturday, while the Baggies will aim to end their recent blip when they host in-form Middlesbrough.

Watford boss Slaven Bilic told BBC Three Counties Radio:

"We played against a good team with the same aspirations but the first half was excellent. They tried to press but we came out of it and were creating spaces everywhere.

"Second half, we expected them to become better and we conceded two, from our point of view, very sloppy goals, but we showed great character and determination, great quality.

"[In our previous game] Against Burnley, maybe we didn't deserve to win that game, but when you concede a 96th-minute goal, you are gutted and that's why we needed a win to make those [last] three draws look better - in the bigger picture, they are four really good games."

West Bromwich Albion boss Carlos Corberan told BBC Radio WM:

"We wasted the first half because we didn't show any of the things we wanted to show. We didn't create any attacks how we wanted to attack and we were not aggressive enough in defence.

"The team played with more personality in the second half and tried to attack more. The spirit we put in the second half was very important.

"The problem is we didn't manage the minutes well after we scored the goals. We didn't protect enough the goals that we were scoring, and that's why, for me, at the end we lost the game."