World number one Karolina Pliskova was forced to dig deep to reach round three of the US Open on Thursday, after qualifier Nicole Gibbs put up a superb fight in a gripping encounter at Flushing Meadows.
Gibbs had failed to win a single game in her last meeting with Pliskova, back in 2015, but took the opening set convincingly on this occasion, overwhelming her opponent with a battery of winners.
Knowing that defeat would see her lose top spot in the rankings, Pliskova gradually raised her own level but was pushed hard before completing a 2-6 6-3 6-4 victory.
World number 127 Gibbs finished the match with more winners and fewer unforced errors, but the most important statistic went against her.
There was much to admire from the underdog's performance, particularly in a first set that she dominated.
An aggressive approach continued to reap rewards for Gibbs as she initially kept pace with her rival in set two through a succession of crowd-pleasing winners, predominantly off the forehand wing.
However, the home favourite eventually faltered, three unforced errors in a row handing Pliskova a break in game eight and reward for her own improving efforts.
Despite falling 0-30 down as she served for the set, Pliskova was able to level the match having successfully challenged a line call that had gone against her at 30-30.
The tension then rose in an enthralling start to the decider, both players saving break points as the momentum ebbed and flowed.
It was Pliskova who ultimately prevailed, breaking convincingly for 4-3 before twice holding serve with ease to book a third-round meeting with either Risa Ozaki or Zhang Shuai.
Pliskova  bt Gibbs 2-6 6-3 6-4
Pliskova - 29/29
Gibbs - 32/28
Pliskova - 11/7
Gibbs - 4/5
BREAK POINTS WON
Pliskova - 2/3
Gibbs - 2/9
FIRST SERVE PERCENTAGE
Pliskova - 66
Gibbs - 59
PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Pliskova - 78/43
Gibbs - 71/55
Pliskova - 87
Gibbs - 82