The 17-year-old was playing her first Grand Slam quarter-final but led 4-0 in the second set, a frustrated Gauff smashing his racquet on the clay after double faulting.
Gauff brought her opponent closer in the opening set, with Krejcikova needing a dramatic tiebreaker to gain the upper hand in the game.
In the second set, the Czech player stepped up the pressure on her younger opponent, winning the first five matches without a reply.
But the American has shown experience to deny her age, saving several match points and winning three straight games to make things nervous before Krejcikova won the decisive ninth game of the second set to reach the semi-finals.
“Already for me it’s something I never dreamed of. I was playing a really great game and Coco is amazing – she’s 17, it’s amazing.”
The two players were playing their first quarter-finals of the Grand Slam in singles. Reaching the bottom eight, Gauff had become the youngest woman to appear in a Grand Slam quarterfinal since 2006.
Despite his age, Gauff, 17, was not unworthy on the big stage of the court Philippe Chatrier.
The No.24 seed held a 3-0, 5-3 lead in the first set, but Krejcikova hit back, saving five match points before eventually winning the 72-minute set.
Gauff identified the loss in the first set as the turning point of the game.
It really seemed to give the world number 33 a boost.
She looked much more comfortable in the second set, handling the ball at will, with Gauff struggling to gain momentum.
And led 5-0 in the second set and only needed one more game to reach her first Grand Slam singles semi-final, it felt like a formality for Krejcikova with Gauff appearing shaken.
However, Gauff showed remarkable strength and resilience in saving multiple match points to win three straight games and suggests that a previously unthinkable recovery may well be possible.
But it was not and on Krejcikova’s sixth match point the Czech player won the match after an hour and 50 minutes.
Krejcikova believes some of her singles successes are due to a change in perspective during the Covid-19 shutdown.
“It came to my mind. I was like, well, I go and I go and play tennis and I lose, but there are actually people who lose their lives. I felt more like, just relax because you’re healthy. Just enjoy it and just enjoy the game. You can do something that other people might like to do too, but they can’t. “
Krejcikova will face defending champion Iga Swiatek or Greece’s Maria Sakkari for a place in the final at Roland Garros.
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