After 2 hours and 40 minutes, Victoria Azarenka finally slotted an angled passing shot past Zhu Lin to seal a 4-6, 6-1, 6-4 victory to book her sixth Australian Open quarterfinal spot.

It was gone 2 a.m., and the two-time champion's relief showed in her face, her exultant scream of joy and her gracious words for her opponent afterward.

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"She never gave up, no matter what the score was," Azarenka said. "With this tennis, she has to be Top 20, because she played amazing. I'd never heard of her before, I know she's coming from China -- but there are so many players who can come out here and produce an amazing level.

"Sometimes it helps when you know your opponent, but I didn't know much about her and I had to adjust on the go. Today was blinding for me. She's an amazing player, I wish her luck for the rest of the year and I hope we'll see a lot more of her."

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No.87-ranked Zhu was making her first appearance in the second week of a major, and for the second match in a row following her third-round upset of No.6 seed Maria Sakkari the Chinese player thrilled a late-night Melbourne show court by going toe-to-toe with a higher-ranked player.

After struggling to read the direction and pace of Zhu's compact strokes initially, Azarenka adjusted over the course of numerous multi-deuce battles to pull through a the match in which she tallied 41 winners to her 28-year-old opponent's 45.

"I feel so relieved," Azarenka said. "It was 2 hours and 40 minutes of complete pressure point by point, momentum shifts, there was everything in this match.

"I'm so happy I was able to manage it. At the beginning of the year there were a couple of very close matches that didn't turn my way, so I'm very happy that I took my chances. I was down 15-40 [in the last game] and I was like, 'You have to take it, nobody's going to give it to you.' I'm very proud of myself for that."

Australian Open: Azarenka survives Zhu in late-night three-setter