Kenneth Zohore's double and a Junior Hoilett goal secured an easy victory against a Leeds side whose captain Liam Cooper was dismissed before halftime after picking up two yellow cards.
Kemar Roofe scored Leeds' consolation goal late on but they fell to a second defeat in three Championship games.
Welsh side Cardiff have 23 points from 10 games, three ahead of Leeds and Wolverhampton Wanderers, who play on Wednesday, and four ahead of Preston North End who beat Hull City 2-1 away thanks to Callum Robinson's late goal.
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Ipswich Town sit a point further back in fifth after they thrashed struggling Sunderland 5-2 to arrest a slump of three defeats in four league games.
The Black Cats, relegated from the Premier League last season, have won once in the Championship all season and are in the bottom three with six points from a possible 30.
Bristol City registered a 2-0 victory against bottom side Bolton Wanderers to climb to seventh -- one point ahead of Aston Villa who thrashed Burton Albion 4-0 away.
Middlesbrough missed the chance to move into the top six as they lost 1-0 at home to mid-table Norwich City, while Fulham won 3-1 at Nottingham Forest.
Millwall scored two late goals to beat visiting Reading 2-1, Brentford netted a late equaliser in 1-1 home draw against Derby County while Barnsley and Queens Park Rangers finished 1-1.
Third-placed Wolves can move level on points with Cardiff if they beat sixth-placed Sheffield United on Wednesday.
(Reporting by Tom Hayward; Editing by Ken Ferris)
