Three biggest upsets on Day 2 of U.S. Open

Day 2 of the 2024 U.S. Open saw top-ranked men's players Jannik Sinner, Daniil Medvedev and Carlos Alcaraz coast into the second round with comfortable first-round wins. Similarly, top-seeded women's stars such as Iga Swiatek, Elena Rybakina and Jessica Pegula got off to triumphant starts.

However, the action-packed day of tennis was not devoid of a few significant upsets.

World No. 11 Stefanos Tsitsipas (Greece)

The former two-time Grand Slam finalist fell to World No. 84 Thanasi Kokkinakis, 7-6(5), 4-6, 6-3, 7-5, after a three-hour, 55-minute battle at Grandstand. Australia's Kokkinakis fired 47 winners to Tsitsipas' 44 and seemed in total control of the match after a hard-fought tiebreaker to win the first set.

Tsitsipas has struggled to make noise at Flushing Meadows since losing to Carlos Alcaraz in their epic five-set showdown in 2021. Since that loss, he's gone 1-3 at the North American major. In fact, Tsitsipas has never advanced past the third round at the venue, a surprising outcome considering his impressive record on other hard court surfaces, which includes a trip to the finals of the 2023 Australian Open.

The 25-year-old Greek star was in the news earlier in August for his publicized split with his coach, his father Apostolos. Tsitsipas' first major without his father by his side didn't end on a good note.

World No. 11 Danielle Collins (USA)

The 2022 Australian Open finalist was knocked out by fellow American Caroline Dolehide following a 1-6, 7-5, 6-4 loss. The result was particularly shocking after Collins breezed to a first-set win and was up a break in the second. However, a few unforced errors on her part allowed the younger Dolehide to seize control. After the match, Collins refused a bouquet of flowers in honor of her impending retirement. The 30-year-old made it clear she didn't want the attention.

While Collins is eliminated, several top-ranked Americans remain alive in their home major. That list includes Coco Gauff, Jessica Pegula, Taylor Fritz, Tommy Paul, Ben Shelton, Frances Tiafoe and Madison Keys — all of whom won their first-round matches to advance on Monday/Tuesday.

World No. 10 Jelena Ostapenko (Latvia)

While a loss to a former four-time major winner and World No. 1 Naomi Osaka isn't technically "an upset," Ostapenko entered the contest seeded 10th against the unseeded Japanese star. Osaka — who skipped most of 2022 and 2023 with injuries and maternity leave — only returned to the Tour earlier this year and hadn't looked her old self since.

However, Osaka showed flashes of a former two-time U.S. Open winner on Tuesday, dominating Ostapenko with a 6-3, 6-2 win to set up a second-round clash against Czechia's Karolina Muchova.

As for Ostapenko, the 2017 French Open winner was likely caught off guard running into an opponent of Osaka's caliber in the first round. The unusual event obviously worked against her.