Rickie Lambert's 35th-minute free-kick proved enough to seal a 2-1 win at St Mary's after an early opener from Jay Rodriguez had been cancelled out by a header from John Terry.
Chelsea's shock loss allowed Tottenham to leapfrog into third place with a 2-1 win at Swansea.
More top news
Jon Platt's conviction brings to an end a legal battle over unauthorised term-time absences that went all the way to the Supreme Court.
Simon's Blog - Bugs
Friday night's forecast for the west of the region