Second-seeded Iga Swiatek has not lost before the last 16 at this level since Cincinnati 2021.

The Pole was 5-2 up in the first set but Mertens fought back to make it 5-5 before Swiatek was able to regain her dominance in the tie-break.

Swiatek didn't look back from that point on as she made short-work of the second set and she acknowledged she had struggled on her serve. Her first service percentage went from 60% to 79% in the second set.

"In the first set, my serve wasn't working perfectly. I'm glad I was patient enough to just work for it, and in the second set I felt much better," Swiatek said.

Ukrainian Elina Svitolina, the 22nd seed, overcame 15th-seeded Czech Karolina Muchova to move into the fourth round with a 6-2, 3-6, 6-2 win.

In the men's draw, Bulgaria's Grigor Dimitrov battled to a 6-7 (7/3), 6-4, 7-5 win over Karen Khachanov in a contest in which the baseline predictably dominated.

The 33-year-old's victory, secured over two hours and 38 minutes, made Dimitrov the fourth active player to tally 100 Masters 1000 hard-court wins.

"It's great. Last year I think I hit 100 wins indoors, now this. It's beautiful I think every time you hit such a milestone," said Dimitrov.

"We know each other very well, we practice with each other a lot, so there weren't really secrets. At the end of the day, it came down to a few points."

Later on Sunday, fourth seed Novak Djokovic is in action against Argentine Camilo Ugo Carabelli.