Tottenham Hotspur have ended Chelsea's 13-game winning streak in the Premier League with a 2-0 victory at White Hart Lane.
Dele Alli was the hero with headers either side of half time as the Blues surrendered their 100% record since October 1 in tame fashion.
They remain five points clear at the top of the standings but Spurs now sit in third, seven points adrift of their London rivals and ahead of both Manchester City and Arsenal.
Chelsea could have taken the lead as early as the fifth minute when Nemanja Matic floated a pass over the defence to release Eden Hazard, but the attacker's first-time volley was dragged wide of the far post.
Spurs soon began to establish control of the match but it took until the 22nd minute for their first chance to come as Victor Wanyama fired wide of the post from 25 yards.
Moments later, Christian Eriksen created a similar opportunity for himself but like his teammate, his effort just evaded Thibaut Courtois's far post.
Chelsea responded with a David Luiz free kick which was always going over the crossbar, while Diego Costa was also guilty of firing off target from the edge of the penalty area.
It was Spurs who would end the opening 45 minutes on top and soon after Eric Dier had forced a solid intervention out of Courtois at the back post, Alli gave the home side the lead when he headed Eriksen's pin-point delivery into the far corner from 12 yards.
Chelsea returned for the restart very much on the front foot, with Costa being denied from 20 yards by Hugo Lloris and Hazard heading wide from close range when he should have scored.
Spurs had struggled to get going during the opening stages of the second half but on 54 minutes, they doubled their advantage when Eriksen once again found Alli inside the penalty area and the England international was able to head in at the back post.
The visitors required an immediate response if they were to get back into the game and give themselves a chance of prolonging their lengthy winning run, but they barely threatened Lloris's goal for the following 20 minutes and it was Spurs who looked most likely to net a third goal in the match.
Eriksen has struggled for goals in recent weeks but he came inches away from finding the bottom corner with a free kick from 30 yards, while the constant pressure applied by both Alli and Harry Kane always kept Chelsea on the back foot.
Chelsea's only threat on goal in the closing stages came from a Luiz header which was directed high over the crossbar, and their defeat in North London will give encouragement to their rivals that the title race remains alive after they missed the chance to go eight points clear of second-placed Liverpool.
