Dayana Yastremska beat Czech Linda Noskova 6-3 6-4 on Wednesday to book a semi-final spot at the Australian Open, becoming the first qualifier to reach the last four since 1978.
Battling in 30 degrees Celsius (86 degrees Fahrenheit) heat, the Ukrainian's powerful forehand eventually overcame the 19-year-old Czech, who was the youngest player left in the women's draw.
They traded breaks early in the first set, but it was Yastremska who took the lead in the eighth game when Noskova netted a backhand.
Despite failing to get nearly half her first serves in, the Ukrainian kept the pressure on with a string of forehand winners throughout the match.
Noskova failed to capitalise on a break point when she was down 5-3 and Yastremska wrapped up the first set in 36 minutes with another well-targeted forehand.
Both players went off court after the first set, escaping the heat, and Noskova had a long chat with her coach on her return.
The players were level-pegging throughout the second set until the seventh game when Yastremska locked it up on her third break point with a backhand winner that left Noskova stranded on the far side of the court.
She closed out the match on serve when Noskova's backhand return hit the net, ending the Czech's bid for her first tour singles title.
World number 93 Yastremska, who has already beaten two Grand Slam champions during the tournament, next faces either 12th seed Zheng Qinwen of China or Russian world number 75 Anna Kalinskaya, who play their quarter-final later on Wednesday.
Zheng finds groove to down Kalinskaya, reach Australian Open semis
Zheng Qinwen shook off a sluggish start to outclass Russian Anna Kalinskaya 6-7(4), 6-3, 6-1 on Wednesday and reach the semi-finals of the Australian Open for the first time where the Chinese 12th seed will take on Ukrainian qualifier Dayana Yastremska.
Kalinskaya appeared nervous in her first Grand Slam quarter-final as she gifted the opening break of the match with a double fault but Zheng returned the favour immediately and the duo were locked until the tiebreak after more shaky displays on serve.
US Open quarter-finalist Zheng came under pressure when she hit a forehand wide to hand Kalinskaya two opportunities to take the opening set and the Russian finished it with a big backhand.
But Zheng broke her 25-year-old opponent for a 5-3 lead in the next before levelling the contest at one set apiece playing top quality tennis and pounced again without losing a point in the third game of the decider to pull away for the victory.
