Ukraine's Dayana Yastremska in action during her fourth round match against Belarus' Victoria Azarenka [Source: Reuters]

Qualifier Dayana Yastremska continued her fairytale run into the quarter-finals of the Australian Open on Monday with a 7-6(6) 6-4 upset of twice former champion and 18th seed Victoria Azarenka.

The Ukrainian world number 93, who stunned Wimbledon champion Marketa Vondrousova in the first round, had to fight hard but was rewarded for her aggression with 38 winners to forge on into a half of the draw devoid of top 10 seeds.

In a punishing baseline battle with virtually no net play, Yastremska got the first of the six breaks of serve in the opening set only for Azarenka to rattle off the next four games to edge in front.

Azarenka, back-to-back champion in 2012-2013 and a Melbourne semi-finalist last year, served for the set but Yastremska kept up the pressure through five deuces and finally converted her fourth break point to force a tiebreak.

The tiebreak was just as tight but the Ukrainian sealed it with her 21st winner, a blistering forehand that was just too fast and too deep for 34-year-old Azarenka.

Both players took lengthy bathroom breaks after the first set and Belarusian Azarenka came out firing, racing to a 3-0 lead almost before Yastremska had time to catch her breath.

The Ukrainian stalled Azarenka’s progress and then went back on the attack, finding her rasping winners again to win five straight games.

She held her nerve serving for the match two games later, lashing across one more big backhand to set up a meeting with Czech world number 50 Linda Noskova in her first Grand Slam quarter-final.