Ukrainian top seed Elina Svitolina was made to work hard but triumphed in more than two hours against Viktoriya Tomova as she booked her Monterrey Open quarter-final spot on Thursday.

Svitolina won 7-6 (7-3) 3-6 6-2 over the Bulgarian qualifier in two hours and 24 minutes, having trailed 2-0 in the final set, before rattling off the final six games to set up a last-eight meeting with fifth seed Camila Osorio.

The Ukrainian won the title at Monterrey in 2020, with her victory on Thursday maintaining her unbeaten record at the event.

"It was an extremely tough match today," Svitolina said during her on-court post-match interview. "I think Viktoriya played a really good match, and I had to really fight back in the third set to bring back my best game and try to come back in the match.

"In the end, I managed to win six games in a row, so it's a good effort for me. It was an extremely tough first set, second set didn't go my way, and then the third set I was 0-2 down. I was not playing my best, but I was fighting, until the very end.

"And you know, the Ukrainian flag [in the crowd] really helped me today to fight... I was really fighting until the end, and I found my game in the end."

Last week's beaten WTA Abierto Zapopan finalist Marie Bouzkova maintained her good form with a 6-4 6-2 victory over Petra Martic.

Sixth seed Nuria Parrizas-Diaz won 6-4 7-6 (7-2) over Briton Heather Watson, while Wang Qiang defeated Mayar Sherif 6-0 6-7 (2-7) 6-3.