The American star has now won 12 consecutive grand slam matches following her victory at the US Open last year. This was certainly her biggest test of the tournament so far and the first time that she has dropped a set in Melbourne.
Finding herself 1-5 down in the first set, Gauff faced set points at 5-2 and then again at 6-5 in the tie-break, but a series of unforced errors from Kostyuk handed the 19-year-old American an early advantage.
The pair traded breaks throughout a tight second set, and this time it was Kostyuk who triumphed in the eventual tie-break to force a decider.
Gauff raced into a 5-0 lead but, despite dropping a serve late on, saw out the match to advance to the third grand slam singles semifinal of her career.
“Really proud of the fight I showed today,” Gauff said in her post-match interview. “Marta is a tough opponent. Every time we play, it is a tough match, and yeah, I really fought and left it all out on the court today.”
Gauff, the fourth seed at the Australian Open, now has a 10-0 record this year and will next face defending champion Aryna Sabalenka after the Belarusian defeated Czech Republic’s Barbora Krejčíková 6-2 6-3.
With temperatures exceeding 30 degrees Celsius (86 degrees Farenheit) in Melbourne, both Gauff and Kostyuk had to wrestle with difficult conditions during the three-hour, eight-minute match.
It was Kostyuk’s first grand slam quarterfinal and she trumped Gauff in the winner-count – 39 to 17 – but conceded 56 unforced errors, including 26 in the first set.
The miss that will haunt her most came when she had a set point in the first-set tie-break, only to driver a mid-court forehand into the net.
“I’m here to grow, to learn, to be better,” the 21-year-old told reporters after the match. “Very proud of myself. I won for myself today, and I think that’s the most important thing. It’s just the beginning of the season. Looking forward to what’s ahead.”
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