Bale glanced home a header from Rafael van der Vaart's corner to open the scoring, before Roman Pavlyuchenko missed a penalty for the home side.
However, he made amends when he headed home a Bale cross shortly before half-time and when Pavlyuchenko's shot was parried by Paul Robinson, Peter Crouch followed up to make it 3-0.
Bale added a fourth 15 minutes from time, before Ryan Nelsen and Gael Givet netted late consolation strikes for Rovers.