Five-time champion Serena Williams raced into the fourth round of the Australian Open, demolishing Hungary's Greta Arn for the loss of just two games on Saturday. Williams totally dominated the world number 92 to win 6-1, 6-1 and move into a fourth round clash against unseeded Russian Ekaterina Makarova. The 32-year-old Arn started well and had a break point in the opening game, but that was as close as the Hungarian got as Williams stepped up to overpower her opponent and run away with the match in just 59 minutes. Williams broke Arn twice in the first set and three times in the second as the Hungarian wilted on the big stage of a grand slam centre court. Williams, playing only her second tournament since the US Open last September, said she still had some way to go before she was fully match fit. "I'm nowhere near where I want to be, but I'm trying to play through it," she said. "I'm really rusty -- I'm just trying to play through the rust." The 30-year-old American won the Australian Open in 2009 and 2010 but missed the tournament last year through injury. She is now unbeaten in her past 17 matches at Melbourne Park.