The Blues go into next Thursday's return leg with a slender 1-0 advantage after Oscar came off the bench to produce a moment of magic and score the only goal of the game at the Generali Arena.
Following a first half in which we had dominated without making the breakthrough, the game appeared to be heading towards a stalemate as Sparta Prague defended deep, and in large numbers, after the break.
Eight minutes from time, however, the Brazilian swung the balance of the tie in Chelsea favour with what could prove to be a crucial away goal, his fifth in Europe this season, latching on to an Eden Hazard flick and finishing smartly.
We now have only a few days to recover before we welcome Brentford to Stamford Bridge for our FA Cup fourth round replay on Sunday, a game we now approach in good spirits after back-to-back wins.
Rafael Benitez made three changes to the team which beat Wigan Athletic last weekend. In defence, Ryan Bertrand came into the side at the expense of Ashley Cole, while in midfield, Ramires partnered Frank Lampard with David Luiz missing through suspension. Marko Marin and Juan Mata, both late substitutes at the weekend, started, but John Terry, Cole and Oscar had to be content with places on the bench. Demba Ba was unavailable after representing Newcastle United earlier in the competition.
It was a confident start by the Blues, who began the game on the front foot. Hazard appeared to be brought down right on the edge of the penalty area inside the opening couple of minutes only to see his appeals for a free-kick fall on deaf ears, while a minute later Lampard forced Tomas Vaclik into the first save of the game.
Our quick, incisive attacking play, particularly on the break, was causing Sparta Prague all manner of problems early on, with Marin and Hazard instrumental.
Sparta v Chelsea
The duo combined down the left-hand side with a clever exchange of passes, but as the Belgian raced into the box he dragged his shot across the face of the goal.
As an attacking force, the hosts had been fairly quiet, but David Lafata, making his competitive debut for Sparta, will feel he should have done better when he met a cross from the right and volleyed high over the bar.
Lafata had been the most prolific marksman in the Czech top flight for the past two seasons, and his movement during the opening exchanges suggested both Branislav Ivanovic and Gary Cahill would need to remain alert.
The home supporters were appealing for a penalty after 25 minutes when Cesar Azpilicueta and Ladislav Krejcl went shoulder-to-shoulder inside the box after the Spaniard had displayed a terrific burst of pace to recover. In truth, it was an ambitious shout, and one that referee Daniele Orsato quite rightly waved away.
As the half wore on the home side were gradually beginning to ask questions of the Blues defence, but 11 minutes before the break we should have broken the deadlock.
Marin picked out Hazard, who in turn found the marauding Mata; the Spaniard then helped it into the path of Torres, but the striker couldn't get enough power behind his shot and was thwarted by the feet of Vaclik.
Sparta v Chelsea
Marin's start to his Chelsea career had been dogged by injury, but after scoring his first goal against Wigan and also netting for the Under-21 side on Monday, the confidence was flowing through the German in what was undoubtedly his most impressive display in a blue shirt thus far.
At the other end, however, the warning signs hadn't subsided, and it was Lafata again going close eight minutes before the break, pouncing on a cross from the right and firing inches past Cech's left-hand post.
Both sides emerged for the second half with no changes to personnel, and it was Sparta who had the first sight of goal, Matej Hybs shooting straight at Petr Cech from long-range.
We were enjoying plenty of possession but, unlike during the opening 45 minutes, attacks were tending to break down in the final third.
There was no doubt that Sparta had spoken at the break of the need to limit the supply to our creative players, and their new-found approach appeared to be working.
With 22 minutes left to play Benitez made his first substitution of the night, introducing Yossi Benayoun at the expense of Marin, who looked to be tiring.
It took until the 69th minute for us to trouble Vaclik, as Lampard headed straight into the arms of the goalkeeper from Mata's cross, and as the clock ticked down it became clear that one goal would probably be enough to win the game.
With nine minutes remaining Benitez made a second switch, replacing Mata with Oscar, and it was a substitution which paid off within a minute.
With his first touch of the ball Oscar collected it in his path, before exchanging passes with Hazard on the edge of the box, easing away from his marker and drilling his strike into the bottom corner of the net.
Sparta v Chelsea
It was a goal which came at the perfect time, and while we'd struggled to create many clear-cut opportunities during the second half, on the balance of play it was probably deserved.
Shortly after we almost doubled our advantage as Torres forced a magnificent save from Vaclik with a powerful strike which looked destined for the top corner, but with only minutes remaining the main priority was ensuring we didn't concede.
Chelsea (4-2-3-1): Cech; Azpilicueta, Cahill, Ivanovic, Bertrand; Ramires, Lampard (c); Hazard, Mata (Oscar 81), Marin (Benayoun 67); Torres.
Unused substitutes: Turnbull, Cole, Ferreira, Terry, Ake.
Scorer Oscar 82
Booked Cahill 40
Sparta Prague (4-3-3): Vaclik; Zapotocny, Svejdik, Holek, Hybs; Husbauer (Bednar 84), Vacha, Matejovsky (c); Kadlec, Lafata (Kweuke 75), Krejci (Pamic 81).
Unused substitutes: M Cech, Vidlicka, Polom, Janos.
Booked Husbauer 66
Referee Daniele Orsato (Italy)