The defeat on Thursday means Ange Postecoglou's side are now trailing Aston Villa, who are in the fourth and final qualifying spot for next season's Champions League, by seven points and now have just a single game in hand.
Goals from Trevoh Chalobah and Nicolas Jackson enabled Mauricio Pochettino to emerge victorious against his former club and enhance his team's own chances of qualifying for Europe.
This was far from the Spurs that Postecoglou has built, nowhere near their fluid, swashbuckling best, and rarely did they put serious pressure on a Chelsea backline that had already posted the club's worst league defensive record in more than 30 years.
Instead, it was Spurs' rearguard that looked uncertain and frail.
First, Chalobah was afforded a clear run at Conor Gallagher's cross in the first half as Chelsea stole into a deserved lead, then with 18 minutes to go Son Heung-min and Pierre-Emile Hojbjerg did little but stand and watch as Jackson pounced when Cole Palmer's 30-yard free-kick thudded off the underside of the crossbar.
Chelsea climbed to eighth, their highest position since Pochettino was appointed in July and with realistic hope now of reaching the Europa League -- but Tottenham's top-four ambitions look increasingly unlikely.
Chelsea were bright from the start. Noni Madueke, fresh from his goal against Villa on Saturday, went close midway through the half, skipping infield from the right touchline, stepping across two Spurs defenders and hitting a shot that cleared the bar by inches.
Then came the opening goal. Gallagher's free-kick sailed over everybody, and around the back stole Chalobah, leaping and arching a header high over Vicario and in. VAR checked for offside and for a foul by Marc Cucurella, but the goal stood.
The lively Mykhailo Mudryk sent a curling effort fractionally beyond a post but Spurs did get a chance just before halftime when Romero got free at the back post from Pedro Porro's free-kick but thudded his header wide.
Then Chalobah dived in to deflect Pape Sarr's effort behind, but they were rare openings for an uncharacteristically blunt Spurs attack.
For 15 minutes after the break, Postecoglou's side hemmed Chelsea in their own half, but summoned little in the way of genuine threat.
James Maddison was summoned from the bench to try and light a Tottenham spark, but Chelsea continued to chase, harry and hound, crowding out what little space opened up in their defensive half.
Cucurella was fouled by Dejan Kulusevski 30 yards out, and Palmer's audacious free-kick cracked the bar before Jackson was first on the scene to earn the decisive second.
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