Leylah Fernandez reached the quarter-finals of the Monterrey Open with a battling three-set win over Qinwen Zheng.

Last year's US Open runner-up came through 6-1 4-6 7-6 (7-3) in two hours and 42 minutes to continue the defence of the title she won last March.

Fernandez won a marathon second game on her eighth break point and consolidated that break with a second to go 5-1 ahead in a one-sided first set.

She served out the opener at the third time of asking, but Zheng was beginning to find her feet in the contest and threatened the Fernandez serve early in the second set.

Zheng's first break points finally came at 5-4 and she took her chance to level the contest against the 19-year-old.

But Fernandez outlasted Zheng in a tense decider that went the distance after both players held serve, the second seed aggressively attacking her opponent to take the tie-break 7-3.

Fifth seed Camila Osorio ended the challenge of home hope Marcela Zacarias, meanwhile, the Colombian winning 7-6 (7-3) 6-3.

She will next face either top seed Elina Svitolina or Viktoriya Tomova in the last eight.

Brazil's Beatriz Haddad Maia was a 6-2 6-2 winner against Xinyu Wang and will contest a quarter-final against either Marie Bouzkova or Petra Martic.

Sara Sorribes Tormo was also a straight-sets winner in Wednesday's action, the fourth seed easing past Harmony Tan 6-2 6-2.