(Reuters) - Croatian eighth seed Petra Martic survived another sloppy display to see off Grand Slam newcomer Varvara Gracheva 6-3 6-3 on Friday and reach the U.S. Open round of 16 for the second consecutive year.
Martic, who struggled through an error-riddled match against Kateryna Bondarenko in the second round, was again often her own worst enemy, allowing her 20-year-old Russian opponent to stay in the contest.
The match got off to a ragged start with three straight breaks before Martic managed to hold serve and grab a 3-1 lead.
While Gracheva continued to pile up the errors, Martic began to settle into the match, holding her serve and breaking the Russian a fourth time to take the opening set.
However, it was more of the same in the second with the pair trading breaks before Martic took control, moving into a 4-1 lead and holding on for an uneven win.
After victories over two players outside the top 100, Martic will have to clean up her play with Grand Slam champions Naomi Osaka, Petra Kvitova and Angelique Kerber lurking on her side of the draw.
(Reporting by Steve Keating in Toronto; editing by Ian Chadband)