The Black Cats' 4-2 victory was mired in controversy as they recovered from a 2-1 half-time deficit to claim a second successive league win and provide real hope of avoiding the drop.
Sunderland's victory took them above neighbours Newcastle on goal difference and within a point of Swansea, who were reduced to 10 men when Kyle Naughton was sent off close to half-time with the score 1-1.
Graham Scott, a late replacement for Andre Marriner on Monday, was taking charge of only his fourth top flight fixture - and the Oxfordshire official was in the spotlight most of the night with several big calls to make.
Defoe's first two goals despite him being perilously close to offside on both occasions, while Scott awarded Swansea a first-half penalty which appeared generous in the extreme - then sent off Naughton in contentious fashion.
Sunderland were gifted the perfect start after three minutes when Lukasz Fabianski's loose ball was collected by Adam Johnson and his pass found Fabio Borini
The former Swansea striker's shot was too hot for Fabianski to hold and Defoe was on the spot to tap into an empty net to score against the Welsh club for the third consecutive game.
Swansea were visibly shaken and it almost got worse when Patrick van Aanholt raided down the left to deliver a cross which the unmarked Johnson sent carelessly wide.
Had that gone in it might have been a long way back for a Swansea side, who had started the evening as the joint-lowest scorers in the Premier League.
But they were handed a lifeline after Andre Ayew provided proof that he was in the mood by meeting Gylfi Sigurdsson's corner and flashing a header just wide of the post.
Three minutes later the Ghanaian broke into the box and won a dubious penalty decision after appearing to kick the floor in the act of shooting.
Wes Brown was adjudged to have made the most marginal of contact, but Sigurdsson stroked home the penalty with the minimum of fuss.
Swansea were reduced to 10 men when Naughton was punished for a 37th minute challenge on Yann M'Vila, his studs showing but the defender clearly took the ball and the theatrical reaction of the France international did him few favours
However, Ayew almost instantly sprinted into space, shrugged off Lee Cattermole and buried a powerful low shot through the legs of Billy Jones and into the far corner of the net
Swansea manager Alan Curtis instantly withdrew Leon Britton on the occasion of the midfielder's 500th appearance for the club as Angel Rangel filled Naughton's right-back position.
But Sunderland were level four minutes after the restart as van Aanholt's drive took a telling deflection off the back of Federico Fernandez and flew past Fabianski off a post.
Jermain Lens struck a post from a tight angle as Sunderland came on strongly and Defoe put them ahead just after the hour when he was adjudged onside from Johnson's pass and finished expertly.
Rangel was not so fortunate when he bundled the ball home after Vito Mannone had spilled Sigurdsson's deflected shot on his goal-line.
And Sunderland wrapped up the points when Defoe was again in the right place to finish van Aanholt's cross from a few yards out four minutes from time.
Source : PA