Drogba proved the matchwinner in the Champions League semifinal first-leg win.
"He's in great form, the big man," said Cahill, who was glad to be on the same side as the Ivory Coast striker.
"When I played Chelsea before, I was never on the end of a positive result. He had a hard job playing up front on his own and at times he was a little bit isolated.
"I thought he did brilliantly for us - and defensively, he helped out with the number of times he was in the box next to me clearing headers away.
"He's obviously up there with the best forwards in the world when he's in that form."