New manager Andre Villas-Boas had insisted before the game that the Blues were not further than ever from realising Roman Abramovich's dream of European glory.
But they did little to show on Tuesday night that they were about to end their billionaire owner's eight-year quest until a moment of inspiration from marauding defender Luiz midway through the second half.
The deadlock might have been broken earlier but for another night to forget for £50million misfit Fernando Torres, who at least ended the evening on a high by setting up both goals.
Torres was bought to help win the Champions League, with Villas-Boas recruited for the same reason, and the 33-year-old at least proved his tactical acumen with game-changing substitutions for the third home match running.
The Portuguese's team selection said everything about his priorities in what is his biggest week since taking charge, with neither captain John Terry nor Frank Lampard in the starting XI ahead of Sunday's crunch Barclays Premier League trip to Manchester United.
The Blues suffered their season-defining slump when both were injured last term, so it was something of a gamble to leave them out.
The same could be said about the recall of Torres, who got his wish to play alongside Mata and Daniel Sturridge despite the club's probe into an interview which quoted him appearing to criticise his other team-mates.
Torres would have been licking his lips when Sturridge swung in a second-minute cross which he hooked narrowly over in what proved a frantic opening.
Both sides then saw goals controversially disallowed, Omer Toprak's header from a corner ruled out for pushing and Torres' flick denied by an offside flag against Raul Meireles, who tried to backheel the ball home.
Torres' flick had set up his new team-mate but the frustrations that go with a run of one goal in 22 games soon emerged.
The striker was booked for an an ugly late lunge on Simon Rolfes before missing a golden chance to end his drought when he hesitated trying to convert Mata's 10th-minute cutback.
After a 15-minute lull in which Chelsea struggled to cope with Leverkusen's incessant pressing, Torres fluffed his lines again when well placed before slicing horribly high and wide from 25 yards.
The impressive Sturridge showed his team-mate the way by almost catching out Bernd Leno with rasping near-post drive, nearly beating the goalkeeper to Jose Bosingwa's cross, teasing Gonzalo Castro into a booking and driving a long-range blast just past the upright.
Mata also shone once again, his free-kick on the stroke of half-time nodded straight at Leno by Branislav Ivanovic.
Ivanovic was needed at the other end 10 minutes into the second half, a crucial interception denying Andre Schurrle, who then created a gilt-edged chance for Michael Ballack, Petr Cech racing off his line to block the former Chelsea star's shot.
Torres had also nodded straight at Leno, while Luiz was booked for hauling back Schurrle, who poked straight at Cech after being played in by Stefan Kiessling.
But the save of the night came from Leno, who brilliantly turned Sturridge's first-time finish from Ashley Cole's cross onto the post.
Villas-Boas then raised eyebrows by taking off Sturridge and Meireles for Lampard and Nicolas Anelka, while Leverkusen responded by throwing on Renato Augusto for Ballack.
It was Villas-Boas' changes that reaped instant rewards.
Luiz surged forward from the back, fed Cole, who found Torres, and the striker laid off for the former to find the bottom corner from 15 yards.
Kiessling might have equalised when he sent a diving header wide but Chelsea's tails were up, Anelka wreaking havoc and Mata forcing a brilliant fingertip save from Leno.
Luiz, who earlier hurt himself making a tackle, was withdrawn to a standing ovation, with Alex coming on before Anelka was denied what looked a perfectly legitimate headed goal by an offside flag.
Chelsea endured a nervy finish before finally exploiting the space in behind when Torres squared for Mata to slide home.