Serena Williams into Australian Open third round

MELBOURNE: Third seed Serena Williams brushed aside any injury worries to sweep into the Australian Open third round on Thursday with a straight sets defeat of Garbine Muguruza.

The 15-time Grand Slam winner, gunning for a sixth Australian title, rolled her ankle on Tuesday but was moving freely in the 6-2, 6-0 defeat of the Spaniard.

She next plays Japan's Ayumi Morita, who beat German Annika Beck, and if the draw goes to plan is scheduled to meet world number one Victoria Azarenka in the semi-finals.

The world number three and hot tournament favourite twisted her right ankle during a 6-0, 6-0 demolition of Romania's Edina Gallovits-Hall in the first round on Tuesday and needed treatment.

The injury clearly restricted her movement and she shifted a scheduled training session from court 17 to the indoor facility at Melbourne Park away from prying eyes on Wednesday, fuelling speculation about the injury.

But Williams, who has admitted she's eyeing the first calendar-year Grand Slam since 1988, showed little sign of the problem in her workout against Muguruza, although the ankle was heavily strapped.

Williams had never before played the 112th-ranked Spaniard, who was making her tournament debut, and she raced to a 2-0 lead before some uncharacteristic forehand errors allowed Muguruza to hold servce and get off the mark.

The American wasn't at her best and even hit herself in the face with her racquet in the sixth game as she went for a lob at full stretch, spending the next game dabbing at her lip.

But she rallied to break once more for 5-2 and held for the set.

The second set opened with a marathon 18-minute game, with Williams finally prevailing to break. Any fight left in the Spaniard disappeared with the American taking only 19 more minutes to reel off the last five games. (AFP)