Manchester United's lead at the top of the Premier League is down to five points after the defending champions lost 1-0 at Wigan while Manchester City hammered West Brom 4-0.
Wigan's Shaun Maloney curled home a superb winner four minutes after the break in yet another game marred by controversial decisions.
Victor Moses had a goal disallowed, United were denied a penalty as an eight-match winning run came to an end and even the corner from which the hosts grabbed their first victory in 15 attempts against United was questionable.
But it's a result that breathes new life into the title race, and lifts Wigan out of the relegation zone.
City took full advantage of United's unexpected slip, Carlos Tevez scoring for the first time in 11 months in a routine victory over the Baggies.
Sergio Aguero struck twice and David Silva was on target as City showed why they were once firm favourites for the Premier League crown.
Arsenal strengthened their grip on third place - and the automatic Champions League place it brings - with a 3-0 victory over 10-man Wolves.
Robin van Persie scored the opener from the penalty spot after Wolves' on-loan defender Sebastien Bassong was sent off for bringing down Theo Walcott, who added a second a minute later.
Yossi Benayoun netted the third after the break, and the Gunners are now five points clear of Newcastle and freefalling Tottenham - and seven clear of Chelsea - with five games to play.
For Wolves, though, relegation looms after a seventh straight defeat left them nine points from safety.
QPR's survival hopes were given a huge boost as they impressively dispatched Swansea 3-0 at Loftus Road.
The embattled Rs were unable to match the visitors' slick passing game in the opening 45 minutes and were guilty of some poor finishing.
However, QPR captain Joey Barton made amends in first-half stoppage time when he smashed home the opener.
Jamie Mackie's deflected effort doubled the Hoops' advantage 10 minutes after the restart and Akos Buzsaky wrapped up three points from range.