Marta Kostyuk is through to her first WTA singles decider after defeating Danielle Collins 6-4 6-3 in Saturday's ATX Open semi-final.

Ukraine's Kostyuk prevailed in a closely contested battle against the highest seed remaining in the field, taking the only break of the first set after saving four Collins break points the game prior.

The two women traded breaks to begin the second set, but the 20-year-old Kostyuk was too strong down the stretch, winning five of the final six games.

It will also be the first WTA-level final for her opponent, with unseeded 22-year-old Russian Varvara Gracheva overcoming American Katie Volynets 6-4 5-7 6-4.

The two-and-a-half-hour clash was tight all the way through, with Gracheva only narrowly edging the total point count 101-94.

Meanwhile, down south of the border at the Monterrey Open, world number five Caroline Garcia won her semi-final against Elise Mertens 6-3 6-4.

The reigning WTA Finals champion will have a chance to collect the 12th singles title of her career, and her first of the season, when she meets Croatia's Donna Vekic in the final.

Vekic, the third seed, emerged the 7-5 6-2 victor against China's Zhu Lin, continuing a red-hot run of form that has seen her win 13 of her past 15 matches dating back to New Year's Eve.