The 29-year-old has been strongly linked with a move away from Spurs this summer, despite of being the only senior striker at the club.
Defoe scored in Spurs' opening day defeat at Newcastle.
"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."