Matt Smith and Danny Pugh scored second-half goals as Leeds inflicted a 3-1 defeat on strugglers Birmingham, who slipped into the bottom three of the Sky Bet Championship for the first time this season.
It was the 17th successive home game in which Birmingham have failed to win and highlights their current desperate position.
The Blues played with plenty of commitment until a tragic two-minute spell when Smith and Pugh displayed superb finishing.
Their tale of woe was completed when Paul Caddis turned a Ross McCormack cross past his own goalkeeper in the 78th minute.
Substitute Federico Macheda popped up with an 83rd-minute goal but it was only a consolation effort.
Leeds’ win was their third in four games and they have all come against struggling teams - Blackpool and Barnsley - in the bottom four.
In the process, they completed the double over crisis club Birmingham following a 4-0 success at Elland Road.
Meanwhile, Leeds boss Brian McDermott claims he is not frustrated about stories of him losing his job and being replaced by former Sheffield Wednesday, Bradford and Aston Villa winger Benito Carbone.
McDermott said: “I spoke to Bernie on Friday. He was a really good player but I do not know him.
“These sort of things do not frustrate me or unsettle me. The most important thing is Leeds United and what is best for this football club and what is best to take this club forward. That is the only agenda I’ve got.
“The future is looking brighter as we have won three of our last four games. We were top five at one stage but we had a lot of things going on with the ownership, which was really difficult.
“These are mitigating circumstances and not excuses. We are now as safe as houses in this league and looking to do well next season.”