Five-time Australian Open champion Serena Williams called her shock fourth-round defeat "disastrous" on Monday -- and said she would have served better left-handed.

The 6-2, 6-3 loss to 56th-ranked Russian Ekaterina Makarova was one of Williams' worst at a grand slam, second only to her defeat at the hands of fellow American Jill Craybas in the third round at Wimbledon in 2005.

The 30-year-old made 37 unforced errors and sent down seven double-faults as she was broken five times overall, ending a 17-match unbeaten streak at Melbourne Park stretching back to 2009.

"I served, I don't know. I can't even describe how I served to be honest," she said. "It wasn't good, though.

"My lefty serve is actually better than that. Maybe I should have started serving lefty... I just did not serve well. It was just disastrous really."

Williams injured her right ankle in Brisbane this month, but she refused to blame the injury, or the hot weather, for her listless display, although she did admit movement was difficult and she was "not 100 percent".

"I made 37 errors, that kind of tells the story of the match," she said.

"It was definitely hot out there. I guess I just didn't move the way I wanted to. I tried. It was definitely harder to move to that (left) side."

"You know what, I never blame any injury that I have because I feel like she played really well and she deserved the win today," Williams added.

Williams, a 13-time grand slam winner, was expected to cruise past Makarova, despite the Russian's surprising win over seventh seed Vera Zvonareva in the third round.

But almost from the first point it was obvious Williams was not her usual self as mistakes came thick and fast from her racquet and she moved sluggishly around the court.

"I honestly think (the loss) was on my racquet. I hit a lot of errors. I mean, she hit some great shots down the line but every ball that came, I just hit it as far out as I could," Williams said.

The Brisbane tournament was Williams' first since the US Open last September and she said taking an injury into the Australian Open had made compensating for her lack of court time more difficult.

"Usually I play myself into the tournament, but I don't (usually) have a huge problem with an injury, so this is a completely different situation," she said.

"Usually it's easier for me to play myself in because I'm usually physically OK."