Simona Halep fought back from a set down to defeat Russia's Ekaterina Alexandrova 3-6, 7-5, 6-4 in her Cincinnati opener on Wednesday.
Wimbledon champion Halep, seeded fourth, earned a late break in the penultimate game of the final set to reach the third round after two hours of action.
The Romanian has finished runner-up in Cincinnati three times, last reaching the final a year ago against Kiki Bertens.
In the next round, the 27-year-old, who retired injured from her Toronto quarter-final against Czech qualifier Marie Bouzkova last week, will face either Madison Keys of the United States or Russia's Daria Kasatkina.
"It was a very, very tough match," Halep said. "She played well, hitting the ball very strong.
"Mentally, it was tough to return for me at the start after playing injured last week.
"But I didn't have pain, which is good. It took time to get a rhythm and then do something on court."
She went up a break in the third set, before letting the lead slip, only for the 43rd-ranked Alexandrova to serve two straight double-faults and fall 5-4 behind. Halep completed her fightback on a second match point a game later.
"After the first set, I felt I could play aggressive," she added. "I also changed the tactics.
"I fought and did not give up. I wanted to run for every ball, it felt really good."
Ninth seed Elina Svitolina, a semi-finalist four years ago, advanced past Belgian Elise Mertens 6-4, 6-1.
In the men's draw, Kei Nishikori lost to fellow Japanese Yoshihito Nishioka 7-6 (7/2), 6-4.