Unseeded, these four players brought their A-game on Day 2 of the US Open.

The last time Pospisil defeated a Top 10 player was 2017 Indian Wells, when he upstaged top-ranked Andy Murray. Out this season until Wimbledon due to a back injury, the Canadian had just two Challenger wins, against an unranked player and world No. 422. Khachanov produced a semifinal run in Montreal with quality wins over Wawrinka, Auger-Aliassime and Zverev, and hoped to reach the second week here for the first time. Pospisil survived, 4-6, 7-5, 7-5, 4-6, 6-3, to notch just his second win in 11 major appearances (2018 US Open) and next faces Tennys Sandgren, who rallied from two sets down against Jo-Wilfried Tsonga.

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Unseeded & Unfazed: Pospisil, Kalinskaya lead charge on US Open Day 2

Unseeded & Unfazed: Pospisil, Kalinskaya lead charge on US Open Day 2

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The Russian qualifier had never won a major main draw match in four previous attempts but pulled out a remarkable performance to stun the 2017 champion, 6-3, 6-4. Kalinskaya, ranked No. 127, was efficient when opportunities presented themselves, converting three of four break points. Pushed to deuce in the final game, she closed out the victory in 83 minutes. For Stephens, the last-minute reunion with coach Kamau Murray did not change her poor run of form, as she finished the North American hard-court swing just 1-4.

Unseeded & Unfazed: Pospisil, Kalinskaya lead charge on US Open Day 2

Unseeded & Unfazed: Pospisil, Kalinskaya lead charge on US Open Day 2

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The Austrian came in with questions about his health after a virus forced him out of Cincinnati. While Thiem was not at 100%, Fabbiano still stepped up in the sport’s biggest stadium to handle the moment – and opportunity – to eliminate a Top 10 player for the second consecutive major (d. Tsitsipas in Wimbledon first round). The Italian’s event preparation didn’t go as planned, having been hit off the court by Andrey Rublev in his lone tune-up at Winston-Salem, but he remained steady and determined to oust Thiem, 6-4, 3-6, 6-3, 6-2, breaking open their quarter of the draw.

Unseeded & Unfazed: Pospisil, Kalinskaya lead charge on US Open Day 2

Unseeded & Unfazed: Pospisil, Kalinskaya lead charge on US Open Day 2

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It remains to be said that Muguruza has been struggling all season long, and nowhere near the level that delivered two major titles. Regardless, Tuesday proved to be an impressive display of patience for Riske. The 29-year-old made the most of a clean slate in the second set to post a 2-6, 6-1, 6-3 victory, ending a five-match losing streak at Flushing Meadows. Riske is enjoying a memorable summer, having defeated then No. 1 Ashleigh Barty on her way to the Wimbledon quarterfinals before marrying Stephen Amritraj a week later in her hometown of Pittsburgh, PA. Riske will meet 2017 French Open winner Jelena Ostapenko in the second round.

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Unseeded & Unfazed: Pospisil, Kalinskaya lead charge on US Open Day 2

Unseeded & Unfazed: Pospisil, Kalinskaya lead charge on US Open Day 2

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The Spaniard had advanced to his first major semifinal at Wimbledon and hard courts are generally his most reliable surface. But Kukushkin was an opponent clearly comfortable on the courts at the USTA Billie Jean King National Tennis Center, having advanced to the third round in his past two showings. When Bautista Agut forced a fifth set, favor seemed to shift in his direction with a 3-0 record in deciders this season. Kukushkin however, rose to the occasion by going three for three on break points to dent his foe's major debut as a Top 10 player.

Unseeded & Unfazed: Pospisil, Kalinskaya lead charge on US Open Day 2

Unseeded & Unfazed: Pospisil, Kalinskaya lead charge on US Open Day 2

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Unseeded & Unfazed: Pospisil, Kalinskaya lead charge on US Open Day 2

Unseeded & Unfazed: Pospisil, Kalinskaya lead charge on US Open Day 2

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