Mirra Andreeva celebrated her 16th birthday on Saturday by setting up a Madrid Open showdown with world number two Aryna Sabalenka and admitted: "I have nothing to lose".
The Russian teenager, ranked a lowly 194, eased to a 6-3, 6-3 victory over Magda Linette to reach the fourth round having already ousted 2021 US Open finalist Leylah Fernandez and world number 14 Beatriz Haddad Maia earlier in the tournament.
"I didn't expect to be here and playing Sabalenka in the round of 16," Andreeva told Tennis Channel.
"I'm not really surprised with my level, because I know the way I can play on the court … but of course, I didn't expect to be here and go this far."
Andreeva broke Polish player Linette, world number 19, for 2-0 in the first set, and although the 17th seed broke back, the Russian did it again for a 4-2 lead and served it out.
The youngster broke again in the first game of the second set and converted her second match point to break Linette again and clinch victory.
Andreeva, a wildcard, became only the third 15-year-old to win a WTA 1000 main draw match when she beat Fernandez on Wednesday.
She finished as runner-up at the junior Australian Open in January, while Sabalenka won the women's title for her breakthrough Grand Slam.
"I have nothing to lose," said Andreeva as she looked ahead to facing the Belarusian.
"I just have to go there and show the best tennis I can. There is no pressure at all for me. There is some pressure on her, I think, because she's going to play a 16-year-old girl."
Sabalenka beat resilient wildcard Camila Osorio 6-4, 7-5.
World number six Coco Gauff suffered a surprise third round defeat at the hands of Paula Badosa, losing 6-3, 6-0.
The 19-year-old American, who was runner-up at the French Open last year, broke Badosa in the first game, but the Spaniard battled back immediately to get back on serve, before breaking Gauff again for a 3-2 lead.
Gauff's forehand betrayed her as Badosa broke to love to win the first set 6-3.
The second was a rout with Badosa winning 75 percent of points.
"I think I served very well, I was playing very aggressively from the baseline, tactically I think I played perfectly and I'm very happy to beat a player like Coco," said Badosa.
"I'm working very hard and it's moments like these which make it worth it."
Stefanos Tsitsipas, the 2019 Madrid runner-up, cracked 35 winners to defeat former world number three Dominic Thiem 3-6, 6-1, 7-6 (7/5).
Thiem, now ranked 93 in the world after a lengthy battle with a wrist injury, battled gamely but succumbed on the Greek's fourth match point.
In a remarkable serving performance, fifth-ranked Tsitsipas hit 39 straight first serves from late in the opening set to early in the third.
"That's fantastic, 39 is a lot," Tsitsipas said. "That's a positive mark for me. I think it's just pure relaxation and focus."
World number three Daniil Medvedev saw off Italy's Andrea Vavassori 6-4, 6-3 to also reach the third round.
Vavassori, ranked 164, battled his way past Andy Murray in the first round but could not oust another former world number one in the Spanish capital.
Dusan Lajovic earned a surprise win over world number nine Felix Auger-Aliassime, 6-2, 3-6, 7-6 (7/5).
The Serbian stunned 22-time Grand Slam winner and world number one Novak Djokovic on the way to winning the Banja Luka title last week, as well as beating world number six Andrey Rublev in the final.