Demba Ba scored his first Premier League goal for the club on home soil and his third in 11 days against their opponents before Eden Hazard put the Blues in a comfortable lead before the break with his second goal in as many matches.
But Saints fought back in the second half as Rickie Lambert struck two minutes and 47 seconds after coming on as a substitute before Jason Puncheon grabbed an unlikely point with a wonderful equaliser to push Saints three clear of the drop zone.
Chelsea took an early grip on the game but Ashley Cole only managed a soft header back across goal in the early stages.
They did break the deadlock after 25 minutes though and, almost inevitably, Frank Lampard played a key role and Ba, who had marked his Chelsea debut with two goals in the FA Cup tie, finished.
The Chelsea captain beat Luke Shaw as he jinked his way into the box before laying the ball back for Azpilicueta to curl the cross in. Oscar and Jos Hooiveld both went for the header and the ball deflected up for the Senegalese striker, who executed an acrobatic volley to beat Artur Boruc.
And when Southampton made a hash of clearing their lines, Chelsea pounced for the second. Ramires rifled a shot off the post but Eden Hazard followed up to drill a left-footed shot from the edge of the box past Boruc.
The onus was on the visitors and manager Nigel Adkins threw on Lambert for Rodriguez after 55 minutes. Three minutes later he had scored.
Nathaniel Clyne escaped the attentions of Hazard down the right and swung in a deep cross for Lambert, who found space between three Chelsea defenders to head past Petr Cech for his 10th league goal of the season. No Englishman has scored more.
Chelsea suddenly looked a bit nervous at the back. The Blues had chances to wrap up the game but Ba rifled a spectacular volley over the top and Lampard curled a free-kick wide.
And then, with 15 minutes remaining, Southampton equalised. Youngster Luke Shaw charged 50 yards down the left and pulled the cross back for Puncheon, who teed the ball up with his first touch and powered a volley past Cech with his second.
Chelsea sent Torres on for Lampard to a chorus of boos. The Spaniard rifled one good chance wide and then lofted a cross straight behind for a goal-kick.
Since their 8-0 rout of Aston Villa on December 23rd, Chelsea have lost at home to QPR and Swansea and now drawn with the relegation-battling Saints.