Spurs sealed an 8-0 aggregate success against Dinamo Tbilisi with a 3-0 victory at White Hart Lane in the second leg of their play-off tie, with Defoe scoring twice and Lewis Holtby also on target.
And Villas-Boas hailed the professional attitude of his side as they refused to take their foot off the pedal.
"We couldn't be complacent. All the boys did extremely well," the Portuguese said.
"After a 5-0 win you can come into the game with a laid back attitude. They didn't. They kept their professionalism and got some chances and got some good moments of football with some good combinations."
Defoe faces fierce competition for a starting spot at Tottenham this season and has fallen behind summer signing Roberto Soldado in the pecking order, but his two goals helped take the pressure off Spurs in the second leg.
And Villas-Boas hailed the pedigree of the striker, saying: "Jermain has the goalscoring ability and once again he proved it tonight.
"What we are trying to do is build a strong team with strong players and everyone has to compete for a place.
"We always want to make teams stronger than before so players who are in the top five of Tottenham's all-time goalscorers can only make you stronger."
Despite the comfortable win, the question surrounding Gareth Bale's move to Real Madrid still haunted Villas-Boas.
When asked for an update on the transfer, he said: "No news. This could drag on for a couple of more days.
"I'm not in control of the situation to give you a definite answer."