World number one Karolina Pliskova saved a match point before battling into the fourth round of the US Open with victory over China's Zhang Shuai.
Pliskova, who reached the final last year, had been pushed to three sets in her previous round by qualifier Nicole Gibbs and admitted afterwards she was feeling the pressure.
She was in deep trouble at a set and 5-4 down, with Zhang serving for the match, but she fought off a match point with a fine forehand and recovered to win 3-6 7-5 6-4.
Pliskova took over the number one ranking after Wimbledon despite falling in the second round and has not hit top form since.
Zhang more than played her part in this contest, using the angles well to drag Pliskova all over the court and matching her powerful opponent from the baseline.
She looked set to claim the scalp when she broke in the ninth game of the second set and then created a match point but Pliskova trusted in her weapons and powered a forehand down the line.
The top seed then levelled at 5-5 and broke the Zhang serve again to take the set.
Still it was not straightforward, with 27th seed Zhang going up an early break in the decider, but Pliskova gradually made her extra clout count and with her 33rd winner came the relief of a place in the last 16.
