Sunderland dominated Newcastle from the first whistle but it took until the 45th minute for the deadlock to be broken and it was sure worth the wait as Defoe fired a superb left-foot volley into the top corner.
Dick Advocaat’s men continued to pile on the pressure during the second half but could not find a second goal and they were nearly made to pay as Remy Cabella forced Costel Pantilimon into action for the first time in the match.
The hosts dropped deep in the closing stages as they looked to protect their lead as Ayoze Perez went close but that was all the visitors could muster as Sunderland once again went onto claim the Wear-Tyne bragging rights and a huge boost in their fight for Premier League survival.
Sunderland are unbeaten in their last seven Premier League games against Newcastle but this fifth win will have felt especially sweet.
With all three sides below them picking up points this weekend it was vital Sunderland responded in Advocaat’s first home game in charge and they were the dominant force in the opening stages of the 140th league meeting between the two sides.
However, it was Newcastle with the first real attack and they thought they should have had a penalty after Santiago Vergini’s challenge on Perez.
Referee Mike Dean remained unmoved and it was Sunderland who took control of the game from here on in with the visitors needing the returning Jonas Gutierrez to turn Billy Jones’ cross over his own bar after Seb Larsson’s corner.
Newcastle were struggling to get out of their own half as Sunderland pressed forward at every opportunity and they nearly had the lead, but a combination of the post and Jack Colback kept Connor Wickham’s header out.
Defoe then raced through on goal in the 37th minute but his touch let him down at the vital moment and Tim Krul kept out Wickham’s shot minutes later. But with the half-time break looming, Defoe produced a piece of brilliance to break the deadlock.
The ball was punted long into Newcastle territory and Steven Fletcher leaped highest to grab a flick-on. With the ball dropping from the sky, Defoe hit a blistering volley past Krul and into the top corner to send the Sunderland faithful wild.
The emotion was too much for Defoe as he appeared to be close to tears leaving the field but there were no tears in the stands as the party atmosphere continued long into the half-time interval.
Sunderland continued to pile on the pressure at the start of the second half and a confident Defoe was pulling the strings as his pass found Jordi Gomez, who crossed the ball to Fletcher, but the forward failed to make a decent connection with his shot.
The second biggest cheer of the afternoon was reserved for Colback as the former Sunderland man went into the book after leaving his leg in on Gomez.
Advocaat’s men were starting to enjoy their work and Defoe was in the thick of the action again, clipping the ball into the path of Patrick van Aanholt. The full-back took the ball forward and hit a powerful left-foot shot that failed to trouble the Newcastle goalkeeper.
Sunderland were struggling to wrap things up and when the ball broke to Cabella in the penalty area in the 78th minute the Sunderland fans would have been forgiven for thinking the worst, but Pantilimon was on hand to make a smart save.
Larsson was next to spurn a glorious opportunity for the hosts after excellent work down the left from Van Aanholt and then Vergini’s header was kept out by a scrambling Newcastle defence.
The home side started to drop deep in the final 10 minutes to protect their lead and it nearly cost them. Daryl Janmaat’s flick-on found Perez at the far post and the striker hooked his leg over the ball, but not enough as it sailed into the stands – much to the delight of the home fans.
Five minutes of added time buoyed Newcastle and goalkeeper Krul was sent up in the final seconds for a corner, but Sunderland held on to claim a vital victory in the race to beat the drop.
The win moves Advocaat’s side up into 15th on 29 points, three clear of Burnley, who held Spurs to a 0-0 draw, in 18th.
Sunderland: Pantilimon (7), Jones (7), Van Aanholt (7), O’Shea (7), Vergini (6), Cattermole (7), Gomez (7), Larsson (7), Fletcher (7), Wickham (7), Defoe (8).
Subs used: Johnson (5).
Newcastle: Krul (6), R Taylor (5), Janmaat (6), Williamson (5), Colback (5), Sissoko (6), Gutierrez (6), Gouffran (5), Ameobi (6), Cabella (5), Perez (5).
Subs used: Riviere (5), Armstrong (5).
Man of the Match: Jermain Defoe