The Stamford Bridge side struggled during a pedestrian game but the Brazilian youngster decided the first leg less than 60 seconds after coming on with a delightful finish.
The Brazilian was on the pitch for less than a 60 seconds before he latched on to a delightful flick from Eden Hazard eight minutes from time to notch his sixth European goal of the season and ease the pressure on Rafa Benitez.
The Spaniard rested Ashley Cole and the recovering John Terry but otherwise opted for a strong starting XI featuring the likes of Fernando Torres, Ramires and Juan Mata as he sought to decide the tie with vital away goals.
The away supporters' chants of "Champions League, we know what we are" were a sign of their confidence despite this year's blip, but on this evidence their team is falling short of the performances they became used to last season.
Chelsea probed early with Marko Marin and Hazard combining on the left before the latter's low cross zipped along the six-yard line and away from danger.
The first real chance of the game came for the Martin Hasek's side after a quarter of an hour, with January signing David Lafata skying a free volley on the stretch from 12 yards after a fine ball in from Zopotocny.
Matejovsky blazed an effort over the bar after 26 minutes after a well-worked move from the right again through Zopotocny, and Petr Cech did well to hang onto a deflected shot from Ladislav Krejci a minute later.
Lafata missed another gilt-edged chance on the half hour. The striker beat Chelsea's offside trap but managed to slide a half-volley wide from seven yards out, with only the offside flag to spare his blushes.
Not content with seeing Lafata do all the struggling in front of goal, Torres forced Thomas Vaclik into a low save that was far too comfortable before falling over while trying to finish a pass from Lampard in the area on 37 minutes.
The second half started much as the first ended, with Torres failing to convert another half-chance before the home side began to test the Chelsea back line once again.
Gary Cahill was fortunate to remain on the pitch after clumsily treading on Krejci's heel after 57 minutes having already been booked, with referee Daniele Orsato deciding to be lenient with the England defender, while Marin and Torres running into each other after 63 minutes just about summed up the game for the pair.
The match was in desperate need of a flash of inspiration and substitute Oscar provided it within a minute of his arrival. The Belgium international pulled the ball back wonderfully and the young Brazilian took it in stride before coolly slotting past Vaclik from 16 yards with eight minutes left on the clock.
Sparta was devoid of an answer to Oscar's magic as Chelsea stood firm, and the tie is now firmly in English club's control.