Iga Swiatek had to work to overcome teenager Mirra Andreeva on Saturday with the world No 1 squeezing out a 4-6, 6-3, 7-5 fightback at the Cincinnati Open.
The top-seeded Pole needed a break in the penultimate game of a match lasting more than two and a half hours to finally advance into the semifinals of the WTA and ATP event, a US Open tuneup that concludes on Monday.
Swiatek advanced on her first match point as her opponent drove a return long.
"She's 17, but I feel we were playing at the same level," Swiatek said. "It was a tight match. Every point matters at the end. It was not easy for sure."
Swiatek said that after losing the opening set, she needed a change of tactics.
"I knew I could not play in the same way. I needed to put more pressure on her," Swiatek said.
"I played more proactive and had a better idea of what I needed to do. The same rhythm (as the first set) would not be enough.
"I changed things and felt the results right away."
Swiatek was broken in the third game of the 53-minute opening set and was never able to get it back. Andreeva needed two set points to claim the opener, earning the lead with an ace.
Swiatek struck back in the second set with a break for 2-0, which she held throughout to level the sets at one each.
In the third, the top seed secured the last-minute break for a 6-5 lead and raised her hands in victory as Andreeva returned over the baseline a game later on Swiatek's first match point.