The Australian Open was rocked on Monday when five-times champion Serena Williams was sent packing in straight sets.

Williams, 30, lost to unseeded Russian Ekaterina Makarova, the world No.56, who powered her way to a 6-2 6-3 victory.

Makarova’s win gave her a first career grand slam quarter-final berth.

Williams, who has been nursing an ankle injury, said she would “definitely” not have played this week had she not been competing in a grand slam.

She also said she served “horrendously” with seven double faults and had lost the match off her own racquet with a total of 37 unforced errors.

However, Williams said the positive aspect was that she knew she could improve.

“I just feel like I didn’t play well today. I don’t feel like I can’t get better,” Williams said.

“If I was in a situation where she played so great and I played amazing and I served 80 per cent and I hit no double faults and I didn’t hit 37 unforced errors, that would be a totally different situation.

“I didn’t play well and I’m not physically 100 per cent so it’s just like I can’t be so angry at myself even though I’m very unhappy.

“I can play 100 times better that I did this whole tournament.”

Makarova, 23, took four match points before sealing the fourth-round clash.

Williams had won 41 of her past 43 matches at Melbourne Park and was favoured to go deep into the event.

But she was confounded by the Russian’s power hitting and was continually moved from side to side at impossible angles.

In desperation, the American saved her first match point with an ace.

The second and third, she was given reprieves as Makarova’s returns went long.

But on the fourth, the Russian celebrated when Williams pushed a ball over the sideline.

It was Williams’ first loss to a player outside the top 50 in a grand slam since 2005.

“It’s an amazing feeling, my first time in the quarter-finals,” Makarova said.

“She’s an unbelievable player and it’s great to play against her.”

Makarova meets the winner of the match between fourth-seeded Russian Maria Sharapova and German Sabine Lisicki.

Asked if she thought she could progress even further, Makarova said: “Yeah, I think so, but it’s tough.”

Meanwhile, second-seeded Czech Petra Kvitova will play Italian Sara Errani in a quarter-final after ousting 21st seed Ana Ivanovic 6-2 7-6 (7-2).

Errani made the quarter-finals with a confident 6-2 6-1 win over China’s Jie Zheng.