Defoe scored the only goal of the game on the stroke of half-time, showing fantastic composure to volley home from outside the box.
The strike sent the Stadium of Light into raptures and Defoe was so overcome with emotion that he was in tears as he left the pitch at half-time.
“It was an unbelievable feeling. As soon as it leaves your foot you know it’s going in,” Defoe told Sky Sports. “Words can’t describe how I felt, it was quite emotional for some reason, I don’t know why.
“It was a massive game and I just wanted to do well. The lads have worked so hard and put the effort in, I think that is why it was emotional, I just wanted the three points so badly and I am delighted we got them.”
Asked if it was the best goal he has ever scored, the former Spurs striker said: “One of my best, with my left foot as well. But in a game like this, even if you score a tap-in it’s massive. To score a goal like that is amazing.”
The goal was Defoe’s first in almost two months and secures a fifth straight derby win over rivals Newcastle.
“I was so looking forward to the game, the lads were telling me about the atmosphere what it was going to be like and wow, it was amazing, the fans were brilliant,” said Defoe.
“The team were unbelievable from back to front, everything we had done in training, everything the manager wanted us to do, we did it, and I am delighted.
“Hopefully all the Sunderland fans will be happy tonight and we can kick on and stick together. We still have massive games coming up but if we play like that we will be fine.”