Mertens came from a set down to beat Bartunkova 1-6, 6-4, 6-2 in Monterrey, turning the match around after a difficult start. Her return game lifted her through the final two sets, as she converted five breaks after managing none in the opener.
Bartunkova dominated the first set 6-1, breaking Mertens in game 1 at 1-0, game 5 at 4-1, and game 7 at 6-1. The second set was a tense exchange of breaks: Bartunkova led 2-0, Mertens hit back at 3-2, Bartunkova made it 4-2, and Mertens answered at 4-3 before breaking again at 4-5 to take it 6-4. In the third set, Mertens broke in game 3 at 1-2 and game 7 at 2-5 to close out 6-2.
Total points finished level at 85-85, and both players converted five breaks, but the difference was in the details: Bartunkova hit six aces and six double faults, while Mertens made only two double faults, saved seven of twelve break points and won more second-serve return points (60% to 50%).