The Blues finally had a striker score away from home as Jose Mourinho's substitutions prompted a slew of second-half goals at St Mary's Stadium on New Year's Day
The Blues, who came into the match on the back of wins against Swansea City and Liverpool, flexed their attacking muscle after the break and were simply too good for the Saints, who lost back-to-back home matches for the first time under manager Mauricio Pochettino.
After an entertaining first half, Torres broke the deadlock in the 60th minute, reacting quickly to head into an open net after a deflected Eden Hazard cross beat Southampton goalkeeper Kelvin Davis and hit the post. Chelsea did not have any recognised centre forward score an away league goal in all of 2013 but, on the first day of the new year, the Spaniard broke the drought.
|VIEW FROM ST MARY'S
|By Tom Marshall-Bailey
Chelsea were arguably at their most expressive this season in their win over Liverpool last time out but any remaining critics out there who questioned this side's ability to combine flair with a knack of grinding out results were well and truly put in their place here.
The Blues were fast out the traps but allowed Southampton back into the game and, had it not been for some first-half profligacy, the story might well have been different. As it happened, though, Jose Mourinho's masterstroke of a double substitution early in the second half made all the difference.
The rejuvenated Fernando Torres netted the first, with an opportunistic header from sub Oscar's cross before fellow replacement Willian grabbed the crucial second. Oscar got in on the act with a third as the Blues kept to their end of the bargain in this most fascinating of title races with a performance that underlined their credentials.
Ramires returned from suspension for Chelsea in one of six changes, as the likes of Torres, Juan Mata and Andre Schurrle also came in, while Morgan Schneiderlin and Gaston Ramirez were recalled for Southampton.
Torres started brightly, going close twice in the first three minutes, while Schurrle - making his first league start since scoring twice at Stoke City in December - fired just wide.
Southampton defender Dejan Lovren clashed heads with team-mate Jose Fonte, causing play to stop, and, after the former returned, Pochettino's side grew into the match.
Adam Lallana's close-range shot was blocked by Ashley Cole and the same defender did well to deny Jay Rodriguez when Ramirez played him through with a lofted ball.
For the second time in 12 minutes, Davis was quick off his line to deny Hazard - he did excellently to keep out Ramires earlier - and Lallana was again denied inside the penalty area by an excellent block, this time from Cesar Azpilicueta.
Ramires was a constant threat and, after a charging run, he forced Davis to tip his strike over the bar, while Hazard hesitated when he should have shot in an attacking move that ended with Schurrle's effort blocked.
Lovren and Fonte had efforts blocked as Chelsea failed to clear a corner two minutes into the second half, while, at the other end, Oscar was booked for simulation after a minor collision with the Southampton keeper.
An excellent ball from Hazard set up Oscar - recently brought on for Mata - but, after trying to round Davis in the penalty area, he left a trailing leg in and threw himself to ground.
Chelsea were turning the screw and got their reward on the hour-mark thanks to Torres's quick reaction but Southampton substitute Rickie Lambert fired a warning shot with a close-range header at Petr Cech with 25 minutes left.
Willian linked well with fellow substitute Oscar six minutes later, though, and curled an excellent strike past Davis.
Southampton's high line was punished again when Hazard's ball over the top sent Oscar through and he finished with aplomb eight minutes from time.