Top seed Serena Williams overcame a below-par start to book her spot in round three of the Australian Open with a 7-5 6-0 win over Vera Zvonareva.

Williams appeared short of her best early on in the match, and the advantage was gifted to Zvonareva when the American's double fault handed her the first break.

However, Williams responded quickly to break back immediately with a couple of powerful strokes to put the pressure on her rival.

Chances continued to be offered to the impressive Zvonareva, and after breaking again, the turning point was clear as the Russian wasted three set points in the ninth game.

The response from Williams came as no surprise as the top seed clinched wins in the next four games to secure the opening set.

Zvonareva's start had raised hopes of a shock, but Williams quickly restored order, and she was on the front foot again thanks to four successive games in the second set.

The door was opened to Zvonareva in game five at 0-30 on the Williams serve, but the former world number two, who is currently ranked 203rd by the WTA, missed the chance to keep the match alive.

Another break of serve followed, and that was enough for Williams to continue her bid for a sixth title in Melbourne.