Mata double earns Chelsea valuable victory over Tottenham
Having taken an early lead through Gary Cahill, the unbeaten visitors — without the suspended John Terry — were rocked at the start of the second half when they conceded goals to William Gallas and Jermain Defoe.
However, Mata clinched Chelsea's seventh win in eight league games by equalising in the 66th and then clipping home a neat finish in the 69th.
The Spanish playmaker set up Daniel Sturridge for a late fourth, ensuring Tottenham manager Andre Villas-Boas was unable to gain a measure of revenge for being fired by Chelsea last season after just eight months in charge. The loss ended a run of four straight wins for the home side, and was Chelsea's first victory at White Hart Lane in seven years.
Having beaten Arsenal and now Spurs away, Chelsea are showing a much greater attacking threat this season and look a serious rival to the two Manchester clubs for the title. Roberto di Matteo's side are now seven points clear of City and United ahead of their matches later Saturday.
"It was a test of character today coming here to play a team in form with four consecutive wins," Di Matteo said.
"It was a big derby for us and after the international break there are always a few question marks how you're going to start the new cycle of games, but the answers we gave today were perfect,"
The buildup to the game had been overshadowed by the continuing fallout from the racism case involving Terry, who on Thursday accepted a four-match ban from the Football Association for racially abusing an opponent during a league game last season.
This was the first game of that ban and it was Terry's replacement at center back, Cahill, who put the visitors in front.
A poor headed clearance from Gallas gave Cahill a glimpse of goal and he showed great technique to produce a superb volley that took a slight deflection off Spurs defender Kyle Walker and flew past recalled goalkeeper Brad Friedel.
The goal came in the midst of a spell of concerted domination by Chelsea but the team failed to double their lead and was made to pay.
Gallas, who played for Chelsea from 2001-06, made amends for his earlier error by equalising from barely a yard out after Jan Vertonghen had hooked the ball back into the middle after a searching free kick by Tom Huddlestone.
That came just 63 seconds into the second half and Spurs, who were without Gareth Bale after the Wales winger's wife went into labor, went ahead in the 54th.
Aaron Lennon's driven shot from the angle was heading harmlessly wide when Defoe connected with it with a sweet finish that beat goalkeeper Petr Cech at his near post.
They were the first goals Chelsea had conceded in the second half this campaign but the classy Mata engineered the turnaround.
He pounced on another unsatisfactory clearance by Gallas to drive home an equalizer from the edge of the area and then ran onto a stunning pass by Eden Hazard to beat Friedel with a curling shot.
Having scored his sixth goal in five games in all competitions, Mata then turned provider by crossing for Sturridge — on as a second-half substitute — to tap in and complete the win.
"We are smooth on the eye but we're a good team and showed good team spirit," Di Matteo said.
"We're trying to progress, to develop and become a good team. We have started well, showed the qualities we have - and can still improve on that."