Birmingham-born Troy Deeney bagged a brace as a slick Watford recorded an impressive 4-0 victory at St Andrew's to maintain their promotion charge.
The boyhood Blues fan finally got the better of Jack Butland with a free header in the 38th minute after the England goalkeeper, back on loan at St Andrew's following his deadline-day move to Stoke, had denied the visitors with a couple of fine saves.
Butland could have done better with Watford's second on the stroke of half-time having failed to keep out man of the match Ikechi Anya, although it was no more than the lively winger and the Hornets deserved following an impressive and intricate attacking display.
A well-worked counter-attack saw Anya claim his second assist of the afternoon as he set up Deeney shortly after the hour mark, before Almen Abdi fired home a fourth late on, with the Hertfordshire side further strengthening their position as top goalscorers in the npower Championship.
Three points, which ensured Watford's first league double over Blues since 1988/89, takes Gianfranco Zola's Hornets up one place to third in the table.
Birmingham, however, booed off the pitch at full-time, saw their recent resurgence clinically ended and remain in a relegation scrap.
Pre-match talk was dominated by Lee Clark's decision yesterday to drop striker Nikola Zigic from his matchday squad, with the Blues boss not holding back in his criticism of the Serbian's work-rate and attitude in training this week.
Watford, boosted by around 2,500 travelling supporters, were showing plenty of industry going forward in the early exchanges, Anya first to test Butland after nine minutes.
Although Blues were holding their own albeit without testing Manuel Almunia at the other end.
The game's first real chance came after 22 minutes but Deeney could only head wide Abdi's corner from six yards.
Matej Vydra's neat turn and half-volley was gathered well by Butland at the second attempt before the City goalkeeper superbly saved with his legs from Abdi.
Butland was again called into action to routinely collect Vydra's free-kick although Blues were probing well at the other end, with Chris Burke particularly lively.
Wes Thomas left Nyron Nosworthy and Anya for dead before firing over as Blues' threat increased.
But it was then that Watford broke the deadlock and never looked back.
Nathaniel Chalobah, so commanding in midfield, flicked the ball out to the right for Anya and he crossed for the unmarked Deeney to head home from six yards in front of the Tilton Road Stand.
And the lively Anya doubled Watford's advantage just before half-time, teasing Paul Robinson - yet again - before drilling straight through Butland.
The home side went in search of a quick route back into the game at the start of the second half, Peter Lovenkrands denied from close range before Thomas agonisingly came within inches of connecting with Paul Caddis' cross.
But it was Watford, so clinical going forward, who added a third shortly after the hour mark as a well-worked move finished with Anya squaring for Deeney to convert.
The goal completely ended the game as a contest although Blues continued to press, Curtis Davies and Lovenkrands both going close.
Yet there was still time for Abdi to add a fourth in the closing stages after Butland had parried Cristian Battocchio's effort to the edge of the area.