According to api.tennis, Mertens and Swiatek have met twice. Iga won both matches, in 2024 and 2025. She did not drop a set in either match.
In 2024, Swiatek won 6-3, 6-4. Neither set went to a tiebreak.
The 2025 meeting followed a different scoreline: Swiatek won 7-6(2), 6-1. The players went to a tiebreak in the opening set, while Iga won the next set more comfortably.