Juan Martin del Potro, seeded eighth, also advanced with a 6-7 (6), 6-3, 6-1 win over American wild card Ryan Sweeting. However, Mardy Fish, last year's runner-up, lost to Jeremy Chardy of France, 7-6 (4), 7-6 (1).
Djokovic struggled at the start of the season, but is coming off a tournament title at Dubai last month.
"Winning Dubai meant a lot for my confidence level and for my game overall,'' he said. "I've changed my racquet. Probably that was the big reason for mental instability in certain stages at the start of the year. I was thinking about that more than my game. Luckily for me, it has changed.
"The quality is there. The game is there. The fitness is getting much better. It's just a mental ability to play the best tennis. My confidence has raised in the last month and a half. There is room for improvement, but I'm taking it step by step.''
Fish, who beat Nikolay Davydenko, David Nalbandian and Roger Federer en route to last year's final, had beaten Chardy two weeks ago at Delray Beach, Fla., where he won the title.
But he said Sunday he "really didn't think I played the big points very well. I just missed some shots I haven't missed in the past month. I've been playing some great tennis (recently), really hitting the ball well in practice and coming in here with more confidence than I've had coming into any tournament ever.''
In the women's draw, top-seeded Dinara Safina, No. 4 Vera Zvonareva of Russia, No. 9 Caroline Wozniacki of Denmark and unseeded American Jill Craybas all won their third-round matches.
Safina, who will move to the top of the WTA Tour rankings if she reaches the final round, beat Shuai Peng of China, 7-5, 6-4; Zvonareva, on track for a possible semifinal meeting with Safina, was a 6-3, 6-1 winner over Czech Petra Kvitova; and Wozniacki, Zvonareva's potential quarterfinals foe, beat Kaia Kanepi of Estonia, 6-3, 3-6, 6-3. Craybas, No. 102 in the WTA Tour rankings, ousted Nicole Vaidisova of the Czech Republic, 6-4, 6-3.
