Russian Ekaterina Makarova switched off from tennis during her season break. Unfortunately, for Serena Williams, she flicked the ‘on’ switch at the wrong time.

A lowly world No.56, Makarova rocked the Australian Open on Monday when she powered her way to a 6-2 6-3 victory over the American and into her first career grand slam quarter-final.

The five-time champion has been nursing an ankle injury and 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.

Nevertheless, it was a major upset after the 23-year-old Russian plummeted down the rankings in the latter part of last year.

“I was (ranked) 29 but then, in the end of the year, I lost six tournaments in the first round,” Makarova said.

“I had a good holiday and didn’t think about tennis and then a good preparation.

“I practised so hard with my coach and I think the results showed I worked hard.”

Makarova, for some reason, was confident she would make it past Williams, winner of 41 of her past 43 matches in Melbourne.

“I played her in Beijing and it was really tough but this time, I don’t know, I felt so comfortable.

“I felt like I could beat her. Maybe in my head is what helped me. It was just a different feeling.”

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.

She is scheduled to meet 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.

With every victory, Kvitova is subjected to speculation she will fly out of Melbourne as the No.1.

But the continual probing elicits little more than irritation now.

“Well, I mean, it’s all the time you are asking me,” Kvitova said after her fourth-round match.

“I can say something about this when I am No.1 – not now.”