Peterborough produced the shock of the Championship season so far as they ended Cardiff's perfect home record with a 2-1 victory.
The table-topping Bluebirds had won their opening 10 league games in the Welsh capital but came unstuck against a Peterborough side bottom before kick-off.
Michael Bostwick put Posh ahead after 22 minutes with a superb long-range effort and on-loan Dagenham striker Dwight Gayle netted the second two minutes after the interval. Rudy Gestede's late goal ensured a nervy finish for Darren Ferguson's team, but they held on for three crucial points.
Despite Cardiff's shock loss they stayed top of the division as closest rivals Crystal Palace drew 2-2 at Birmingham.
Prolific striker Glenn Murray fired Palace 2-0 ahead after an hour but they relinquished the advantage as substitute Nikola Zigic (66) and Papa Bouba Diop (82) scored.
Middlesbrough moved three points off the lead with a 2-0 win over Wolves.
Hull are also three points off the top after beating Yorkshire rivals Huddersfield thanks to goals from Robert Koren (eight) and David Meyler (90). Their win was soured when Alex Bruce saw red during a scuffle after the whistle, although he appeared to be retaliating to an elbow from Alan Lee.
Sheffield Wednesday earned local bragging rights with a 1-0 victory over Barnsley which eases the pressure on boss Dave Jones and piles it on counterpart Keith Hill.
The Owls had lost their previous seven games in the npower Championship which left the former Cardiff boss clinging on to his job, but Chris O'Grady's first-half goal earned the vital points and stopped the rot.
The goal was shrouded in controversy, though, as O'Grady tapped home after Barnsley goalkeeper Luke Steele had dropped the ball under the challenge of Gary Madine, with television replays showing a push.
Chris Taylor scored the only goal of the game on 67 minutes as Millwall moved into the play-off places with a 1-0 home win over Leicester.
Watford dropped out of the top six as they drew 1-1 at Burnley. Nathaniel Chalobah's 11th-minute opener was cancelled out by the prolific Charlie Austin from the spot on 28 minutes.
Blackpool beat derby rivals Blackburn 2-0 with goals from Wes Thomas (22) and Kirk Broadfoot (81).
Leeds joined Blackpool in the top half as they won a third successive home league game 2-0 over Ipswich. On-loan winger Jerome Thomas (20) and Paul Green (68) were on target.
David Ngog scored twice in the final 16 minutes as Bolton grabbed a much-needed 2-0 win over Charlton while Derby returned the same scoreline at Bristol City - Jeff Hendrick (34) and Craig Bryson (36) got the goals.
Brighton and Nottingham Forest played out a goalless draw at the Amex Stadium.