Defoe's strike moved him within one goal of Martin Chivers's club-record European tally of 24 and also made it seven goals in four starts this season, but summer signing Roberto Soldado has been preferred to the England international in domestic action so far.
Villas-Boas refused to commit to who would start Sunday's Premier League match against West Ham United, but did reserve special praise for Defoe's achievements at the club.
"We have to judge recovery and the fact that JD was involved today and Soldado wasn't. Everything will come into consideration. We have been extremely happy with the performances of both. It is a question of deciding what is best for the team," Villas-Boas told PA.
"It was another great goal, a great finish. It's really good to see him out there again doing extremely well whenever he's given the opportunity. He is a great professional, has a great attitude and now he's only one off Martin Chivers so it's a real great achievement for him.
"I think he has the ambition this season to go even further up the ladder in this record tally behind Martin Chivers and as an all-time goalscorer so I think that plays highly in his motivation, definitely."
The win was Tottenham's second in as many games in the Europa League proper this season, leaving Villas-Boas's side top of Group K by four points.