At 18, Babos was the youngest player to reach the second round in Monterrey. However, what she lacks in experience, she makes up for in match toughness, proving this against Cirstea by coming from a set down to triumph, 46 64 62.
The win over Cirstea - her first over a Top 50 player - was her 26th in the last 31 matches and this rich vein of form sees her on the verge of breaking into the Top 100 for the first time. Meeting her next is Austria's Patricia Mayr-Achleitner, who defeated Eva Birnerova, 61 63.
Also through to the quarterfinals is Babos' compatriot, Greta Arn. In a match littered with service breaks, Arn's consistency helped her overcome Croatian qualifier Marta Abramovic, 64 62.
"I didn't know Maria beforehand, so I didn't know what to expect from her today. But I was consistent and played well," Arn said. "I've been playing here for three years and know you have to adjust to the altitude, and be more patient and consistent. I was happy with how I adjusted today."
"I've never played Nina Bratchikova but her ranking has improved a lot since the Australian Open," Arn added. "She's fast, hits hard and is really tough. It's going to be a difficult match. I'm going to try my best."
Thursday's other singles match saw Mandy Minella take on wildcard Yaroslava Shvedova. In a match that had more ebbs and flows than the Gulf of México, Minella recovered from the disappointment of throwing away a one set, 3-0 lead to finally see off Shvedova, 63 67(1) 64. Her reward for prevailing in the two-and-a-half hour epic is a first career WTA quarterfinal, where she will face No.2 seed Sara Errani.
Meanwhile, in the doubles competition, Paola Suárez's comeback gathered further momentum as, alongside partner Gisela Dulko, she defeated Abramovic and Mihaela Buzarnescu. Facing Dulko and Suárez in the semifinals will be top seeds Errani and Vinci.