Karolina Pliskova saved a match point before recovering into the fourth round at the US Open with a hard fought victory over Zhang Shuai.
The Czech world No 1, who reached the final in New York last year, required three sets to defeat American home favourite Nicole Gibbs in the second round and was on the brink of defeat before rallying to record a hard fought 3-6 7-5 6-4 success.
Pliskova lost the first set after struggling to gain rhythm in her service games and despite securing an early break in the second set against the Chinese 27th seed she needed to fire a forehand winner down the line to save a match point in the tenth game of the second set with Zhang serving for the match.
Zhang played her part in an absorbing encounter, which opened the schedule on the Arthur Ashe Stadium, taking the initiative in the baseline exchanges and targeting the Pliskova second serve.
The 28-year-old appeared set to knock out Pliskova when she secured a 2-0 lead in the decider but couldn't get over the line as Pliskova, who received for treatment for an arm injury at the end of the second set, upped her game to prove too strong for her opponent.
"I was match point down and I thought I haven't tried many forehand winners down the line. That's what I did. I may not have got another chance," said Pliskova, who maintains her chances of retaining her world No 1 ranking at the end of the tournament.
"She got tight at the end of the second set, so I just waited for my chances."
The Czech, who is battling with Wimbledon champion Garbine Muguruza and Elina Svitolina for the top spot, will next meet American Jennifer Bradyon Monday.
Brady, the world No 91, had never featured in a main draw Grand Slam event prior to this year's Australian Open but the 22-year-old is enjoying a fine run at Flushing Meadows.
In her US Open debut, the home favourite has impressed and secured a hard fought 6-3 4-6 7-6(3) victory over Romania's Monica Niculescu on Saturday.
Latvia's Jelena Ostapenko, the reigning French Open champion, fell to a surprise straight sets defeat against the talented 20-year-old world No 38 Daria Kasatkina.
The Russian secured her spot in the fourth round at the US Open for the first time in her career after securing an impressive 6-3 6-2 victory which included Kasatkina winning 12 successive games at one stage.
Kaia Kanepi will next meet Kasatkina after the Estonian prevailed in a three-set battle against Japan's Naomi Osaka, who defeated defending champion Angelique Kerber in the first round, 6-3 2-6 7-5.
Meanwhile, Lucie Safarova, the women's world No 1 doubles player, was another Czech player to progress to the last 16 with a comfortable 6-3 6-2 victory over Japan's Kurumi Nara and will next meet CoCo Vandeweghe.
The American, who is coached by former Wimbledon champion Pat Cash, showed great resolve and determination to prevail against 10th seed Agnieszka Radwanska 7-5 4-6 6-4 in a match that lasted just shy of three hours.
Elina Svitolina, the Ukranian world No 4, ended the run of American Shelby Rogers in a 6-4 7-5 victory to advance to the fourth round in New York for the first time in her career and awaits the winner of Madison Keys against Elena Vesnina.
Rogers was involved in the longest women's singles match in US Open history on Thursday against Daria Gavrilova but fell short against an in-form Svitolina who won the Toronto title last month.
Sky Sports Tennis will have all the action from the US Open covered via our website www.skysports.com/tennis with our live blogs and updates throughout the fortnight as the Grand Slam year reaches its climax.
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