Dele Alli underlined his growing reputation by single-handedly ending Chelsea's 13-match winning run Wednesday, scoring two headed goals to give Tottenham a 2-0 victory over the Premier league leaders.
The defense has been the bedrock of Chelsea's three-month hot streak but Alli was gifted space to score carbon copy goals in each half at White Hart lane after meeting crosses from Christian Eriksen.
By taking his tally to seven goals in four games, the 20-year-old Alli inflicted Chelsea's first loss since its last trip to north london at Arsenal in September and prevented the Blues from earning a league record 14th successive win in a single season. "This league is very tough," Chelsea manager Antonio Conte said. "Now it's important to restart. After 13 wins in a row it's difficult to accept defeat."
Chelsea still lead liverpool by five points but Tottenham is now only seven points behind in third after a fifth successive victory.
"It's a big statement for us but we are happy to stay under the radar," said Alli, whose team's hopes of a first title since 1961 were ended by Chelsea last season.
Conte established the winning run that sent Chelsea to the summit after switching to a three-man defense to stem the tide of goals in a 3-0 first half collapse at Arsenal.
But the defense is now leaking goals, conceding four in the last two matches after only letting in two in the previous 12 fixtures. Tottenham matched Chelsea's formation and restricted Conte's side to few chances, while proving more cohesive and solid at the back to frustrate the visitors' forward line.
"I didn't get on the ball as much as I would have liked to," Alli said.
The midfielder didn't need to.
Alli was described on the eve of the game by manager Mauricio Pochettino as the "most important player to emerge in English football in recent years." Signed from third-tier club MK Dons two years ago for 5 million pounds (then $8 million), Alli lived up to his manager's exalted praise with his mastery of the attacking spaces.
While Chelsea was looking more likely to score on the counterattack in the first half, Tottenham used a break to devastating effect on the stroke of halftime with Alli making the breakthrough.
Kyle Walker teed up Eriksen and as the cross was floated into the penalty area, Alli was left unmarked between Victor Moses and Cesar Azpilicueta to coolly nod past goalkeeper Thibaut Courtois.
It was an assertive start to the second half by Chelsea, but Tottenham preserved its lead.
Goalkeeper Hugo lloris blocked a low shot from Diego Costa, Eden Hazard's low header was off target and Moses' penalty appeals were dismissed when he was clipped by Mousa Dembele.
Spurs then punished Chelsea's porous defending again in the 54th minute with a replica of the opener.
Walker did the running down the right flank before laying the ball off for Eriksen. The Danish international picked out Alli between Moses and Azpilicueta, and the midfielder found the target with this header.
"We were short of the levels we set ourselves, for whatever reason that may be, a few misplaced passes and not moving the ball as quick as we have been," Chelsea defender Gary Cahill said. "They are a top quality opposition and we got punished for being short."
Chelsea's plight in the derby was summed up in the first half by the team's top scorer, Costa, engaging in an on-pitch row with Pedro Rodriguez for several minutes. It followed Pedro's failure to run into space in front of goal to meet a pass from Costa when the score was still 0-0.
"It is normal disappointment," Conte said. "It was a good chance for us and we wasted it."
Conte not keen on overhaul
Even after Chelsea's 13-match winning run ended, Antonio Conte found something to laugh about.
In the three months since Chelsea adopted the 3-4-3 formation Conte favored in Italy, the team has powered to the top of the Premier league.
So Conte was bemused by the suggestion he might consider abandoning the three-man defense that was penetrated so easily by Tottenham in Wednesday's 2-0 loss but had previously been serving Chelsea so well.
"We found a good balance with this formation and we continue with it," Conte told reporters at White Hart lane. "But it's very strange you ask me after a defeat after 13 wins in a row if I'm thinking of changing the formation.
"I am seeing that to stop us other teams are changing the formation."
Tottenham did just that; adopting a three-man defense and successfully impeding Chelsea, particularly Diego Costa. The league's top scorer has only failed to score in three of Chelsea's last 10 games, including both league meetings with Tottenham now. Costa's 14 goals have helped Chelsea to establish a lead at the summit over liverpool that remains at five points despite the Spurs setback.
Chelsea has conceded four goals in two games - more than in preceding 12 games.
"It's normal to work in one system, one formation," said Conte, the former Italy and Juventus coach halfway through his first season in England. "When you change a lot and use a different system it means you don't work a lot with this formation. Every day you try to improve your system and try to provide different solutions - with the ball and without the ball."
Conte first adopted a three-man defense during his last trip to north london in September when Chelsea was trailing 3-0 at halftime to Arsenal, while already reeling from a loss to liverpool in its previous league game.
The tactical tweak stemmed the flow of goals in the second half at Arsenal. Chelsea responded to the Arsenal loss by going on the 13-match winning run that Tottenham ended to prevent its west london rival from setting a new single-season league record. "We are disappointed but also we must be pleased," Conte said, "because to win 13 games in a row is not easy in this league, and also today we lost against a good team, a really strong team."
Tottenham, whose hopes of a first title since 1961 were ended by Chelsea last season, is seven points behind Conte's side in third place while liverpool is second. And Conte believes Chelsea, champion in 2015 under Jose Mourinho, is more resilient than it was during the September slump.