Story of the match
Birmingham started on the ascendancy in the fixture, as Lukas Jutkiewicz had a 13th minute shot blocked by Ben Wilmot inside the box.
Maikel Kieftenbeld picked up an early booking as Watford looked to frustrate Birmingham with their possession play, with Hornets boss Vladimir Ivić opting for five across the midfield with boyhood Birmingham fan, Troy Deeney solely leading the line.
Both teams failed to make an initial opening, until a strike from Mikel San José from close range cannoned off the post and back into play.
Birmingham looked to continue their momentum, searching for a third consecutive win despite wholesale changes from Blues boss Aitor Karanka. Gary Gardner and Marc Roberts came close to breaking the deadlock, but the score remained level going into the half time break.
The second half commenced and Watford looked more threatening, as Troy Deeney had an attempt in the 68th minute saved well by Neil Etheridge.
Watford forced Birmingham back, winning a penalty in the 84th minute as Stipe Perica was brought down by Kristian Pedersen, resulting in a second yellow card. Deeney took the penalty and scored, securing all three points on the road for Watford who moved back into the play-off places.
Takeaways from the match
The contest was relatively even until the latter stages, as Watford's quality showed by forcing a late breakthrough. Aitor Karanka made multiple changes to his side, and this looked to have affected the team as his side failed to find any real rhythm in the contest.
Player of the match
Deeney is a proven Championship striker, and good strikers take their chances when they're presented with one, showcased by Deeney's winning goal. Watford will look to challenge at the top this season and with the help of Deeney, Ivic's side will be sure to reach their target of a swift return to the Premier League.