Gauff’s US Open title defence ended in the fourth round in September but, after parting with coach Brad Gilbert, she immediately bounced back by claiming the China Open title.

The serve that let her down so badly in New York appeared sharper against Pegula, with the 20-year-old hitting two aces to just two double faults.

Her forehand, arguably her biggest weakness, was still error-prone against Pegula, but Gauff was more solid throughout.

She broke to go 4-2 up and then calmly served out the first set, wrapping it up with a forehand winner.

Pegula struggled for consistency against her good friend, often following up a well-constructed point with an uncharacteristic miss.

She was broken in the first game of the second set and whacked her racquet to the floor in frustration, but that seemed to reset her as she broke back from 40-0 down.

However, four unforced errors in a row from Pegula handed Gauff the break back, and the younger American promptly won four games in a row to clinch victory.

“Sometimes it was sloppy, sometimes it was great – but that’s tennis,” said Gauff.