Defoe has been linked with a move away from White Hart Lane this summer after finding his starts limited last season.
"He always has this killer instinct. He scored in midweek for his country, scored for us during pre-season and again here," said Villas-Boas.
"He is showing that touch that we need up front. Jermain accepts that we are looking for one more striker because the team is in need of that, but when we have them all together the quality of the player is tremendous.
"It is a different situation for him now. I have nothing to do with anything that happened in the past. He is our striker, is playing extremely well, is full of confidence and has been deadly in front of goal."