Chelsea made it a day of misery for former manager Andre Villas-Boas as they stayed top of the Premier League with victory in an enthralling encounter at White Hart Lane.Tottenham boss Villas-Boas was facing Chelsea for the first time since he was sacked in March after only nine months in charge – and for a brief spell in the second half it looked like he would celebrate with three points.Chelsea, without captain John Terry as he started a four-match ban for racially abusing QPR’s Anton Ferdinand, led at half-time through Gary Cahill’s magnificent volley. Spurs, however, reversed fortunes dramatically at the start of the second half with two quick goals from William Gallas and Jermain Defoe.It was a situation that called for Chelsea to show the substance to match the style this reshaped side is offering up this season. They delivered both to secure a hugely impressive win.The outstanding Juan Mata struck twice in three minutes as Chelsea regained the ascendancy and substitute Daniel Sturridge’s simple fourth in stoppage time completed a hugely satisfying performance from the Champions League holders. Spurs were forced into a late change when Gareth Bale dropped out of their starting line-up after his partner went into labour – and it was understandable that they should miss a player of his influence.Nothing, however, can diminish the growing sense that even though this Chelsea team is undergoing something of a transition, they have the quality to be very serious contenders for the title this season.And, in Mata, they have a player of the highest quality as a creator and scorer who was able to cast his spell over this wonderful game.Gallas, who endured a miserable day defensively, wasted a perfect opportunity to give Spurs the lead after only three minutes when he failed to make firm contact with Gylfi Sigurdsson’s free-kick from six yards. Chelsea’s approach and change in personnel allows them a great deal of fluidity. Young Brazilian Oscar is central to this change in emphasis and he showed his threat with a long-range effort that flew just wide. Villas-Boas demonstrated his faith in 41-year-old Brad Friedel by reinstating him ahead of France goalkeeper Hugo Lloris but the veteran was powerless to stop Cahill putting Chelsea ahead after 17 minutes.Gallas’s headed clearance from Eden Hazard’s corner was met by Cahill, who showed perfect technique to send a thunderous volley high past Friedel.Spurs produced a spirited response, with Cech scrambling to save from Defoe, but Chelsea remained dangerous and Mata should have done better than shoot off target after his first effort had been blocked by Friedel.Villas-Boas clearly demanded greater urgency from his players during the break – and he received it as they struck twice in the opening stages of the second period to turn the game around.Gallas scored his first goal for Spurs when he glanced in after Jan Vertonghen hooked back from the far post then Defoe added the second after 54 minutes, turning in Aaron Lennon’s driven cross for his 200th career goal. It was time for Chelsea to demonstrate their own resilience and they did not disappoint, producing two quick goals from Mata to regain the advantage Spurs had taken from them.Another poor clearance from Gallas offered Mata the opportunity to shoot low past Friedel from the edge of the area, then the Spaniard accepted Eden Hazard’s pass to send a composed finish past Friedel.Villas-Boas introduced Emmanuel Adebayor for the subdued Clint Dempsey in an attempt to regain the initiative – but it was fitting that Mata should have a say in the final act as he rolled a perfect cross in for Sturridge to score with ease.