MELBOURNE (Reuters) - Serena Williams overcame a feisty challenge from Ayumi Morita at the start of second set but recovered to swat aside the Japanese 6-1 6-3 and ease into the fourth round of the Australian Open on Saturday.

The 31-year-old American, seeking a sixth crown at Melbourne Park and a third successive grand slam title, was 3-0 down in the second set after suffering a service break for the first time in the tournament.

Showing no discomfort from the ankle strain she sustained in the opening round, however, the third seed stormed back to win the next six games and dismiss the world number 72 in 66 minutes.

Williams, who approached record levels with her serve when she hit the 207 kilometer per hour (129 mph) mark in the first set, set up a last 16 date with Russia's Maria Kirilenko.

(Reporting by Nick Mulvenney, editing by Greg Stutchbury)