Defoe moved to the Stadium of Light from MLS outfit Toronto in January and opened his account for the Premier League club in last weekend's 2-0 victory over Burnley.
The ex-Tottenham striker was on the scoresheet again at the Liberty Stadium with a clinical 18-yard finish shortly before half-time.
Former Sunderland loanee Ki Sung-yueng's second-half header earned Swansea a point, but Poyet believes Defoe's addition has boosted the confidence among a Sunderland team who are now four unbeaten in all competitions.
"With Jermain we are a different team," he said.
"When you have a player you know is sooner or later going to score, it makes the rest of the team believe that they have a chance to win football games so it's a pleasure to have him."
Defoe has hit the ground running despite having not played for three months before his Sunderland debut at Tottenham last month.
Poyet revealed plans to give Defoe a rest at some point after four consecutive starts, but intends to utilise the former West Ham man while he is in top form.
"I've been killing myself thinking do I need to give him a rest because he didn't play, but I'm sorry Jermain I can't - I need him to play," he added.
"He was out when he finished the league [MLS] and he was training on his own and he came and we threw him in against Spurs.
"The idea is to make sure you don't take a big risk but make sure you use him wisely. But you can't let games go past and not play Jermain Defoe. I'm glad we used him and he scored, it means the decision was good for everyone."
