Oscar saved Chelsea, interim boss Rafael Benitez and striker Fernando Torres from embarrassment with an 82nd-minute winner in the Europa League last 32 first leg clash at Sparta Prague.
Torres, a £50 million striker now with one goal in 13 games, missed a straightforward effort after 35 minutes and sliced a second-half shot out for a corner in another impotent display from last season's Champions League winners at the Generali Arena.
With a stalemate looming and the visiting fans' ire for Benitez and Torres increasing, Oscar came on for Juan Mata and scored with his first involvement, netting neatly following a one-two with Eden Hazard.
The result, following last Saturday's 4-1 Premier League defeat of Wigan, saw Chelsea claim back-to-back wins for the first time since December and keep a clean sheet for a second time in eight games.
After inflicting Sparta's first home loss in Europe in 11 matches, despite an unconvincing display, Chelsea now play Brentford in FA Cup fourth round replay on Sunday before the return leg at Stamford Bridge next Thursday.
Chelsea, who suffered the ignominy of becoming the first side to exit the Champions League at the group stage as holders, had not competed in the Europa League since 2002 and were expected to ease by Sparta.
But the hosts were unfazed by the Blues' visit, having beaten Feyenoord and Athletic Bilbao as part of their long unbeaten home run in continental competition.
Benitez was sufficiently confident against a team playing their first competitive game since December 6 to leave captain John Terry, who missed the Wigan win with a knee injury, on the bench alongside Ashley Cole in a side showing three changes.
Terry has started only twice under Benitez, whose faith in Torres remains firm, even though the Spaniard was the only available strike option, with Demba Ba ineligible.
After Frank Lampard's early shot from 25 yards was held at the second attempt by Sparta goalkeeper Tomas Vaclik, Hazard twice tried to engineer an opening for Torres, but on each occasion the World Cup winner did not contest good crosses into the six-yard box.
A promising opening from Chelsea, with Marko Marin lively, subsided quickly before an lapse in defence - all too familiar for Benitez of late - nearly presented Sparta with the opening goal after 17 minutes.
Right-back Tomas Zapotocny's left-footed diagonal pass over a static defence found David Lafata, who lifted the ball over Petr Cech's goal when he had time to control the ball.
Lafata, the Czech league's top scorer in each of the last two seasons, was making his debut after signing from Jablonec in January and was keen to impress, causing Chelsea a concern more than once.
Ladislav Krejci was also a danger and Cesar Azpilicueta had to be alert and swift after the winger had darted into the left side of the box.
Moments later Krejci shot and Cech had to dive to his right to save.
Sparta were finding spaces in and behind the Chelsea defence, but that left them exposed on the counter attack and Chelsea so nearly took advantage after 35 minutes.
Marin found Hazard down the left and the Belgian picked out Mata with a cross-field pass.
Instead of shooting, Mata teed up his compatriot Torres, whose current confidence levels were summed up by a weak toe-poke which did not trouble Vaclik.
Mata and Lampard then combined before the ball fell to Torres, who had slightly over-run it and could not get a shot away in a crowded area.
Lampard shot straight at Vaclik before the break and on the resumption had to make a last-ditch interception to deny Krejci a shooting opportunity.
Chelsea were giving the ball away readily, with Lampard among those culpable, and creating few chances.
Torres headed over a free-kick from Mata, who then crossed for Lampard, who stooped low, but could only head straight at Vaclik.
Torres' evening was summed up when he shot right-footed from 20 yards, the ball slicing high and going out for a throw-in.
Mata made way after 82 minutes for Oscar, who had an immediate impact.
He injected pace into proceedings and received a return pass from Hazard before clinically netting into the bottom corner.
Torres had an effort saved soon after before Ondrej Svejdik headed over from a corner.
Fortunately for Chelsea and Torres that was as good as it got for Sparta as the visitors prevailed.