A banner day for home players at the Hana Bank Korea Open saw two unheralded South Koreans knock out both of the Grand Slam champions in the main draw in the first round. Wild card Back Dayeon came from 5-2 down in the third set, saving one match point, to edge No.2 seed Jelena Ostapenko 3-6, 6-1, 7-6(4) in 2 hours and 13 minutes. Earlier, Jang Su-Jeong had dismissed No.5 seed Sofia Kenin 6-1, 6-4 in 1 hour and 31 minutes.

It was the first time two South Koreans had won their openers in Seoul since 2013, when Jang defeated Klara Koukalova and Ons Jabeur to reach the quarterfinals as an 18-year-old, and Lee Ye-Ra bested Daria Saville in the first round.

Highlights: Jang d. Kenin

Jang's upset of Kenin was her first Top 50 victory since her win over Koukalova, and the first time she had beaten a Top 30 opponent in her career. But it was not the first time she had come out on top against Kenin, having triumphed 7-6(6), 6-3 in their sole previous meeting in the first round of the 2018 Newport Beach WTA 125 event.

Demonstrating strong counterpunching skills and deft touch on the drop shot, No.162-ranked Jang was rarely threatened by the former Australian Open champion. The recently resurgent Kenin was unable to find the consistency that had taken her to the San Diego final and Guadalajara semifinals last month.

No.569-ranked Back had made her WTA main-draw debut by qualifying for Seoul in 2022, and entered the tournament on a hot streak at ITF level. The former Top 50 junior has won 22 of her previous 26 matches coming into Seoul, including two ITF W15 titles and a further two finals. However, Back had never previously faced a Top 200 opponent, and Ostapenko's experience showed as she powered through the first set.

Back's inside-out forehand had been an impressive weapon in the opener, but shifting her tactics towards slice-heavy defense enabled her to turn the match around. Forced into extended rallies, Ostapenko's mistakes began to mount, and the Latvian's final tally of 68 unforced errors outweighed her 43 winners.

Ostapenko, the 2017 champion and 2022 runner-up in Seoul, seemed to have regained her grip on the match as she rattled through four straight games from a break down in the decider to lead 5-2. Back was able to reel her in, though, saving a match point at 5-4 with a forehand pass.

For a second straight year, Ostapenko found herself in a third-set tiebreak with a South Korean wild card ranked beneath 500. But whereas she had survived Jeong Boyoung 6-4, 3-6, 7-6(2) in the 2022 first round, she couldn't pull off a similar escape against Back. Facing match point, an Ostapenko backhand sailed long to give the home player a first tour-level victory.

Back will next face Kimberly Birrell, who advanced 6-4, 6-4 past qualifier Sachia Vickery. Jang will have the opportunity to return to the quarterfinals a decade on against Emina Bektas, who saved one match point to overcome Laura Pigossi 6-7(5), 6-4, 7-5 in 3 hours and 8 minutes.

Highlights: Pegula d. Hruncakova | Lys d. Schmiedlova | Bektas d. Pigossi

No.1 seed Jessica Pegula escaped the rash of upsets, defeating Viktoria Hruncakova 6-2, 6-4. Pegula raced out of the blocks, dropping just five points in the first five games. Though No.112-ranked Hruncakova was able to deliver intermittently breathtaking power, the Slovak was unable to find the consistency to trouble Pegula. The World No.4 will next face 19-year-old Ashlyn Krueger, the recently-crowned Osaka champion, in an all-American second round.