A late Troy Deeney penalty was enough for Watford to win a game of few chances at Birmingham City.
Birmingham-born Deeney converted after Stipe Perica was brought down in the area by Kristian Pedersen, who was also sent off for a second yellow card.
Neil Etheridge could do nothing to stop the spot-kick in the Birmingham goal as Watford secured a first away win in six matches to maintain pressure on the Championship's top two.
Before the late drama, the match had failed to produce much in terms of goalmouth action, with Watford taking more than an hour to register a first effort on target.
Watford, under Championship manager of the month for November Vladimir Ivic, have now lost just once in their past nine matches and stay fourth, four points behind leaders Norwich.
Defeat for Birmingham meanwhile saw them drop a place to 16th.
Their recent resurgence which brought back-to-back victories at promotion contenders Bristol City and Reading also came to an end.
Blues came closest to breaking the deadlock in the first half when Mikel San Jose glanced a Gary Gardner corner on to the post.
Watford host sixth-place Brentford on Tuesday while Birmingham head to Cardiff City on Wednesday.
Birmingham City manager Aitor Karanka told BBC WM 95.6:
“We have been on the end of a few penalties and sending offs, but my main concern is how easy it is we're conceding those penalties as we don't see those sort of decisions going our way at the other end of the pitch.
“We knew today we would be up against Premier League quality team and it would be tough. But we felt we had it in us to win this game and we had it under control.
“We were really consistent and confident with the ball, but when I thought everything was under control, the penalty and the sending off arrived.”
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