Chelsea suffered a stunning slip-up at the top of the English Premier League as they were humbled 3-0 at home by Sunderland on Sunday, dpa reported.
Chelsea had won all their home games this year but they turned in a terrible performance to suffer their worst home loss in the league for eight years, leaving manager Carlo Ancelotti fuming.
"We have to have a meeting about this on Thursday when they come back from the international break," Ancelotti said. "To look at what happened.
"I think this was the worst performance since I've been here. The performance was poor today, but in football it can happen if you're not at your best and don't play with your best mentality.
"All the things were wrong. We didn't play how we wanted to, Sunderland showed fantastic spirit and played better."
Sunday's win lifted Sunderland up to sixth while Arsenal closed the gap in second place to two points with a 2-1 win at Everton.
Chelsea suffered problems just before kick-off when captain John Terry and Alex were ruled out through injury.
And the leaders were barely recognisable from the side that has set the pace this season as they were outplayed by a Sunderland team who won away for the first time this season.
Nedum Onuoha put the visitors ahead on half-time when he weaved his way past three defenders before firing in a brilliant opening goal.
Seven minutes later, Asamoah Gyan finished a fine move to double Sunderland's lead and a horrible mistake by Ashley Cole handed Danny Welbeck a gift of a third goal three minutes from the end.
Bacary Sagna and Cesc Fabregas scored Arsenal's goals at Everton and Tim Cahill's late effort for the home side proved to be too little too late.
"It's always very difficult to come here and that is three very important points, based on great spirit, great resilience - more than style," Arsenal manager Arsene Wenger said.
"These are very important ingredients to be successful. You need those qualities to win the title. The team deserves a lot of credit."
Full back Sagna put Arsenal ahead early in the second half, finishing off after Andriy Arshavin pulled the ball back to him from close range.
Fabregas looked to have wrapped up the points when he slotted in a second but Cahill slammed in a late goal from Everton a minute from time to pour on the pressure.
In the end, Arsenal held on for the win to turn the pressure on Chelsea.