Emmanuel Adebayor poked home a Dempsey cross in the 83rd minute to earn his side a 2-1 win after Dempsey had cancelled out a third minute opener from Steven Nzonzi for Stoke.
Villas Boas said: "He (Dempsey) has been absolutely immense this season with his assisting and his goalscoring and he has sometimes not got the credit he deserves.
"He is a hard worker and a very complete athlete and he had an amazing game. It was an extremely good individual performance.
"We came back from difficult circumstances because part of Stoke's strength is their delivery at set-plays and the delivery (for the goal) was absolutely amazing.
"But we managed to control the other ones and the circumstances turned for us. I am extremely happy for the team in the way we were patient in the game, we kept the ball moving and eventually we got the breakthrough."