Manchester United suffered another significant Premier League setback as Adam Lallana scored an 89th-minute equaliser to earn Southampton a 1-1 draw at Old Trafford.
David Moyes had looked on course to record back-to-back wins for the first time as United boss as the hosts edged ahead through Robin van Persie.
But Saints' enterprise was rewarded in a penalty-box scramble, when Dejan Lovren got his foot to the ball and prodded it goalwards before skipper Lallana got the last touch from a position right in front of David de Gea.
It means United have won only three times from their eight league games so far and the gap to pace-setters Arsenal has now widened to an imposing eight points.
Arsenal moved clear at the top of the Premier League with a 4-1 win over Norwich at Emirates Stadium, with Jack Wilshere scoring an early contender for goal of the season.
The Gunners capitalised on Liverpool's draw at Newcastle with what proved to be a hard-earned victory over a determined Norwich, who could consider themselves unfortunate not to take something from the match despite the final scoreline.
In the end, though, Arsenal's class told as Wilshere opened the scoring with a sublime finish to a slick passing move that cut Norwich open on 18 minutes.
After soaking up plenty of pressure, Germany playmaker Mesut Ozil headed in a second just before the hour, but Jonny Howson reduced the deficit.
Arsenal, though, made sure there would be no late drama when Aaron Ramsey, who had started on the bench, fired past John Ruddy from close range after jinking into the six-yard box.
Ozil stroked in a late fourth to ensure a somewhat flattering scoreline, but it was more evidence that this Arsenal side look set for a long-overdue sustained title challenge.
Jose Mourinho was sent to the stands as Chelsea claimed an eventually emphatic but controversial 4-1 victory over Cardiff to move second in the Premier League.
Chelsea had to come from behind after a mistake from David Luiz allowed Jordon Mutch in to clip the ball over Petr Cech, who was making his 300th Premier League appearance.
Chelsea's equaliser was a result of an error of judgement from referee Anthony Taylor. David Marshall bounced the ball in front of Samuel Eto'o, who simply stuck out a leg to nick it, even though FIFA rules state the goalkeeper is still in possession at that point.
Eto'o then contrived to miss after receiving a pass from Eden Hazard, who netted while the Cameroon striker was on the floor.
But Eto'o did claim his first Chelsea goal midway through the second half and Oscar and then Hazard, with his second, wrapped up victory.
The third and fourth goals came after Mourinho was dismissed from the touchline for berating the officials. Mourinho is now unbeaten in 64 Premier League matches at Stamford Bridge, but few can have been as incident-packed as this.
Daniel Sturridge preserved Liverpool's promising start to the Premier League season by denying ten-man Newcastle a famous victory.
The Reds trailed at St James' Park before the England international headed home Luis Suarez's cross to make the final score 2-2.
Yohan Cabaye had given the Magpies a 23rd-minute lead with a spectacular long-range strike, but the visitors were handed a lifeline when central defender Mapou Yanga-Mbiwa was sent off for hauling back Luis Suarez five minutes before the break.
Steven Gerrard levelled from the penalty spot - his 100th league goal for the Reds -- but Paul Dummett, who had been drafted into central defence in the wake of Yanga-Mbiwa's departure, marked his third senior appearance with his first goal 12 minutes after the restart.
However, Sturridge's effort got the visitors back into the game and the home side had to survive a late onslaught as Liverpool pressed hard in front of an appreciative crowd of 51,703.
Sam Allardyce had a birthday to forget as his West Ham side put on a defensive horror show to help Manchester City to their first away win of the season as the game ended 3-1.
A breakdown in communications between James Tomkins and Winston Reid allowed Sergio Aguero to put City ahead, and slack marking from Ricardo Vaz Te later allowed the Argentine to head home his seventh goal of the season.
Vaz Te made amends by scoring with an acrobatic overhead kick, but David Silva struck ten minutes from time to give Manuel Pellegrini's men a 3-1 win.
Supersub Steven Pienaar scored with his first touch to hand Everton a 2-1 win over Hull at Goodison Park, with Swansea thrashing Sunderland 4-0 and Stoke playing out a goalless stalemate against West Brom.
Kevin Mirallas put Everton 1-0 up after eight minutes. Hull goalkeeper Allan McGregor was culpable, thinking Mirallas' low shot from 25 yards was going wide only to see it go in off the post.
Hull levelled on the half-hour mark through Yannick Sagbo - on as a substitute after Danny Graham was stretchered off - who swept home Sone Aluko's cutback from close range for his first Premier League goal.
Pienaar then put Everton back in front on 57 minutes, less than 60 seconds after coming on, sweeping home Mirallas' cross.
After a goalless first half, Swansea scored three times in less than seven minutes soon after the restart before adding a late fourth to hand Gus Poyet defeat in his first match in charge of Sunderland.
Phil Bardsley put through his own net at the Liberty Stadium on 57 minutes with Jonathan de Guzman doubling Swansea's lead soon after courtesy of a curling, dipping shot from 20 yards. Wilfried Bony then grabbed Swansea's third from the spot after Craig Gardner brought down Leon Britton in the box.
Chico made it 4-0 ten minutes from time after prodding home from a corner. The result leaves Sunderland rock bottom of the Premier League.
Stoke were held to a 0-0 draw by West Brom at the Britannia. West Brom saw a second-half penalty appeal turned down by referee Howard Webb when Charlie Adam appeared to tread on Youssouf Mulumbu's heels in the area.