Manchester City's defence of their Premier League title looks all but over after they pressed the self-destruct button at Southampton on Saturday. Elsewhere, Chelsea, Arsenal and Tottenham all won as the race for Champions League qualification stayed finely poised, while at the other end of the table Reading and QPR suffered disappointing defeats.
Manchester City face the prospect of trailing neighbours United by 12 points at the end of the weekend after they were stunned 3-1 by Southampton - following a catalogue of errors. City's stuttering campaign was hit by Jason Puncheon's early goal before a Joe Hart howler allowed Steven Davis a second, and after Edin Dzeko responded Gareth Barry scored a comedy own goal to leave Roberto Mancini's men in big trouble.
Mancini had talisman Yaya Toure back from the African Nations Cup but was forced to play Javi Garcia at centre-back at St Mary's, and it was his poor positioning that allowed Jay Rodriguez to burst through in the build-up to Southampton's seventh-minute opener. Rodriguez was foiled in front of goal by the recovering Toure, but the loose ball was converted by Puncheon as City were punished for Barry's loss of possession.
The second goal conceded by City was even more inexplicable, as Hart allowed a straight-forward shot from Rickie Lambert through his arms as he looked to gather into his body, and the spill was poked home by the alert Davis inside the six-yard box.
Saints had chances for a third as the visiting defence continued to look shaky, but a breakaway goal from Dzeko halved the deficit just before half-time.
A second-half siege was anticipated, but within five minutes of the restart Barry needlessly steered into his own net under no pressure whatsoever. Facing a two-goal deficit once again, City barely mustered a reply and were deservedly beaten as Saints moved six points clear of the bottom three.
Arsenal were forced to hold onto a slender advantage against Sunderland after an injury to Jack Wilshere and Carl Jenkinson's sending off left them short-handed, but they ultimately succeeded in that task for a 1-0 win.
Santi Cazorla was the eventual match-winner for the Gunners, the Spaniard firing a sweet left-footed strike beyond the impressive Simon Mignolet after good work from Wilshere and Theo Walcott had created the opening.
Arsene Wenger's side dominated proceedings in the first half, playing some lovely football in midfield, but two key second-half incidents disrupted their progress. First, Wilshere was forced off for Abou Diaby after complaining of a thigh injury, and then Carl Jenkinson, booked after nine minutes for a foul on Jack Colback, was given his marching orders for a similarly poor tackle on Stephane Sessegnon.
The ten remaining men still produced some exciting football - Walcott hitting the post in one particular foray into the final third - but Sunderland poured forward at the death, with only some diligent defending - and wasteful finishing - preventing the Black Cats snatching a draw.
Frank Lampard gave another timely reminder of his value to Chelsea, as his late strike confirmed all three points in what eventually turned out to be a 4-1 victory over Wigan at Stamford Bridge.
The Blues looked nervous after the wily Shaun Maloney halved their advantage with 58 minutes gone, but Lampard was on hand to bury a trademark finish from outside the box to give his side breathing space with four minutes remaining. Marko Marin scored in injury time to add an extra emphasis to the final scoreline.
Eden Hazard, who provided the assist for Lampard's strike, had scored just two minutes before Maloney's intervention to put the European champions on course for victory, after the effervescent Ramires had opened the scoring with a powerful run and finish midway through the first half.
Two smartly-taken goals from Gareth Bale proved decisive as Tottenham claimed an important 2-1 win over Newcastle in the day's early kick-off.
Bale - deployed in an attacking role once again by manager Andre Villas-Boas - revelled in the responsibility he was given, opening the scoring in the fifth minute with a pinpoint curling free-kick and then running beyond the Toon defence late in the match to bury a low winner beyond Tim Krul.
Newcastle's earlier equaliser came through Yoan Gouffran, whose first-half shot deflected wildly into the top corner past the completely wrong-footed Hugo Lloris.
Gouffran was later stretchered off after appearing to suffer a serious leg injury in an otherwise innocuous-looking clash with Kyle Walker as Newcastle struggled to create good openings in pursuit of a second goal.
Indeed, it was Spurs who looked the more likely to get the game's fourth goal, with Bale missing out on a hat-trick in injury time as he flailed a close-range shot well over with his less-trusted right foot.
The nature of the task facing Harry Redknapp was underlined at the Liberty Stadium as rock-bottom QPR were hammered 4-1 by Swansea.
Michu - on the scoresheet for the first time in seven games - notched twice in the contest, as Pablo Hernandez and Angel Rangel also found the net for Michael Laudrup's side in what ended up as something of a rout.
Bobby Zamora scored for QPR shortly after half-time to have the travelling supporters entertaining brief thoughts of a comeback at 2-1, but Hernandez's smart slide-rule finish just two minutes later effectively killed off the contest.
QPR remain six points behind 17th-placed Reading, after goals from Robert Huth and Cameron Jerome proved enough for Stoke to pick up all three points in a 2-1 victory against the recent comeback kings at the Britannia Stadium.
A uneventful first half made way for an entertaining second stanza, as defender Huth broke the deadlock with a powerful header from Glenn Whelan's cross with just over 20 minutes remaining.
Jerome then doubled the advantage with a clinical finish with less than ten minutes to go but Reading - particularly when Adam Le Fondre is on the pitch - have proven in recent weeks that they should never be ruled out of contests.
Le Fondre was indeed thrown on in the dying moments to try to rescue something but, despite Adrian Mariappa's 83rd-minute goal from an Ian Harte cross, an equaliser proved elusive.
Finally, Norwich and Fulham played out a drab 0-0 draw at Carrow Road.
The home side had the majority of the chances but failed to take advantage, with new signing Luciano Becchio unable to make anything of some of his side's best openings. Fulham, meanwhile, edged the possession statistics without turning that into clear-cut chances, with Steve Sidwell forcing just about the only save from Mark Bunn from long range.