Seeded no. 8 and ranked No. 47, Samsonova lost the opening set and was a break down in the decider before she found her way back. It is her first semifinal of the season and her first win over a top-10 player in 2026.
Kostyuk, ranked no. 11, arrived in Mexico as the favorite and could have drawn level with Karolína Muchová in the WTA Race by winning the title. She had reached this stage after the forfeit of American wildcard Taylor Townsend in the previous round.
Samsonova had earlier edged out American Kayla Day 7-6 (4), 2-6, 7-6 (5) and beat Frenchwoman Elsa Jacquemot 7-6 (6), 6-2. She will next face the winner of the match between Peyton Stearns and wildcard Sloane Stephens.
WTA 500 Guadalajara, quarter finals
Quarterfinals:
L. Samsonova (8) d. M. Kostyuk (1). 4-6, 6-2, 7-5
P. Stearns d. S. Stephens. 7-6(6), 6-4
C. Bucsa (6) d. S. Bejlek (3). 6-0, 6-4
I. Jovic (2) d. M. Frech (7). 6-2, 6-1
Semifinals:
L. Samsonova (8) vs P. Stearns – not played
C. Bucsa (6) vs I. Jovic (2) – not played
