Chelsea hit top spot in the Premiership as they defeated title rivals Manchester United by a single goal - a Frank Lampard penalty.
If the Blues are to win the title, and they are now four points ahead of United and one in front of Arsenal, then a few more hard-fought victories like this will be needed.
The champions started well enough with Carlo Cudicini forced into a fourth-minute save from Diego Forlan.
Seconds later an error by the Chelsea keeper and a John Terry slip almost gifted United a golden chance, but the Blues gradually took control and after 17 minutes Adrian Mutu had a right-foot effort from just inside the box, although it flew high and wide.
A Lampard half volley, followed by a Ryan Giggs chance were just the prelude to the significant moment of the game.
After 29 minutes, Roy Keane challenged Joe Cole in the penalty area but failed to win the ball and merely succeeded in upending the England midfielder.
The referee pointed to the spot, amid much protesting from the Red Devils, and up stepped Lampard to coolly slot home a low, right footer, which sent Tim Howard the wrong way.
"The penalty was a major decision," lamented United boss Sir Alex Ferguson. "Cole was going away from goal, so obviously I'm disappointed." In the 32nd minute Chelsea should have sewn the game up, but Howard made an excellent stop from a Mario Melchiot flick and Cole then failed to show composure when left with only the goalkeeper to beat five minutes later, chipping the ball over the bar.
If Chelsea had the better of the first half, United took control of the second - but failed to capitalise on their possession.
Blues boss Claudio Ranieri rang the changes, bringing on Jesper Gronkjaer, Damien Duff and Jimmy Floyd Hasselbaink, but it was the home defence that won the plaudits with an almost faultless display.
Ranieri was relieved to hold on for the win, but still failed to jump onto the title bandwagon.
"It's too early to think of the title," said the Italian. "But it's a great result against the champions.
"We created good chances in the first half, but they put us under pressure in the second and the win will give us lots of confidence.
"I did not start with Duff as I felt he was tired but would do a good second-half job, which turned out to be true.
"We are not like United or Arsenal at the moment - we need to be able to control both halves, but we are gelling as a team."