Jose Mourinho suffered a first home defeat as Tottenham head coach at the hands of Chelsea, led by Frank Lampard and inspired by Willian.
Willian and Frank Lampard got the better of their former manager Jose Mourinho as Chelsea seemingly set their Premier League campaign back on track with a 2-0 win at Tottenham in an ill-tempered London derby.
Chelsea's impressive early season form under head coach Lampard had tailed away in the time Mourinho reinvigorated Spurs, having succeeded the struggling Mauricio Pochettino last month.
Indeed, Tottenham would have leapfrogged the Blues into fourth with victory, yet Willian scored twice before half-time - the second from the penalty spot after a remarkable Paulo Gazzaniga error.
Son Heung-min was sent off for kicking out at Antonio Rudiger with 28 minutes left, and Lampard's men cruised to the finish at Tottenham Hotspur Stadium.
The game was interrupted as referee Anthony Taylor addressed the two coaches, however, with Rudiger reporting an incident of racist abuse.
After four defeats in their prior five league matches, this represented a much-needed win for Chelsea, ensuring a four-point buffer to fifth-placed Sheffield United at Christmas - with Mourinho's Spurs back in seventh.
Chelsea lined up with a three-man defence and bossed the opening exchanges, leading through Willian after 12 minutes.
The Brazilian traded passes with Mateo Kovacic following a short corner, shifted the ball away from Serge Aurier and whipped a fierce 15-yard drive across Gazzaniga into the bottom-right corner.
Harry Kane blazed a presentable opening over the crossbar under pressure from N'Golo Kante at the other end, before Son was similarly wasteful from a tight angle on the left.
And Tottenham were made to pay for their profligacy as Chelsea were awarded a penalty in bizarre circumstances in first-half stoppage time.
Gazzaniga charged from his goal and missed the ball completely as he attempted a clearance, instead catching Marcos Alonso high with his boot. Referee Taylor initially gave a foul against Alonso, but the VAR intervened, and Willian tucked away the spot-kick.
Only the linesman's flag spared Gazzaniga further blushes following the restart, as he spilled Alonso's strike at the feet of the offside Tammy Abraham.
The VAR soon stepped in again when Taylor at first failed to send Son off for a petulant kick after clashing with Rudiger, and Spurs scarcely threatened a response.
What does it mean? Apprentice masters former boss
Rookie Premier League coach Lampard had struggled to arrest Chelsea's slump before heading north to Tottenham, but his switch to a back three proved inspired. The Blues dominated possession from the outset while boasting the requisite athleticism in defence to largely nullify the threat of a counter-attack.
Mourinho's men were slow to respond and, thanks to Gazzaniga's moment of madness, the Portuguese's proud record of never having lost at home to a former club was in tatters by half-time.
Willian silences Spurs
Willian is an unpopular figure with Tottenham fans having joined Mourinho's Chelsea rather than their London rivals in 2013, but he had previously struggled to silence the jeers in these fixtures, failing to score against Spurs in 11 Premier League appearances.
He was at the centre of the visitors' best work in his 12th, though, scoring twice. The first finish was clinical, the second - from 12 yards - composed.
Ill-disciplined in defeat
While Chelsea kept their cool, Tottenham imploded - as they famously did when Leicester City claimed the title courtesy of a draw between the London rivals in 2016.
Moussa Sissoko was fortunate to avoid a card for clattering Kepa Arrizabalaga, while there was no explanation for Gazzaniga's unorthodox intervention and no defending Son for his dismissal.
Spurs can at least enjoy Christmas at home, with their next match also at Tottenham Hotspur Stadium against Brighton and Hove Albion on December 26. Chelsea host Southampton later on Boxing Day.