Sunderland climbed out of the bottom three after two goals in three second-half minutes saw them fight back for a dramatic win over Chelsea.
But when Deandre Yedlin’s cross was deflected into his path, Defoe made no mistake – taking a touch to bring the ball under control, then burying it into the net.
Until then, Defoe had been frustrated all afternoon, with his only effort at goal a header against the post that would not have counted anyway, because the flag was already up.
The former England striker showed again how vital he is to their survival hopes with the way he took his winner after 70 minutes.
Jermain Defoe has now scored 15 of Sunderland’s 40 goals this season, and he has earned them 14 of their 35 points.Defoe does the trick – again
The Black Cats host Everton on Wednesday, and are away to Watford on the final day of the Premier League season.
With Newcastle held by Aston Villa and Norwich losing to Manchester United, Sunderland will stay up if they win one of their final two matches of the season.
Chelsea captain John Terry was sent off for a second booking before the final whistle, which brought scenes of celebration from the Sunderland players and fans.
Nemanja Matic found space to restore Chelsea’s lead before Sunderland turned the game on its head after the break.
Diego Costa’s precise finish gave the Blues the lead but Wahbi Khazri levelled with a spectacular volley.
Fabio Borini beat Thibaut Courtois with a deflected shot, before Jermain Defoe swivelled to score a vital winner.