Sloane Stephens, 25, rallied from a set down to beat Anhelina Kalinina and advance to the third round, keeping her hopes for a title defense alive.
The World No.3 secured a 4-6, 7-5, 6-2 victory over Kalinina, who’s ranked 134th, in two hours and 46 minutes.
Kalinina, 21, was the runner-up in the girls’ singles in 2014 and was playing in her first senior Grand Slam tournament after coming through qualifying. The youngster had taken the first set and drew level from 1-4 down in the second set to set the score at 5-5, but Stephens held firm to power to victory.
“I wasn’t playing my best,” Stephens said. “It was super hot and that was no fun at all. I was sweating a lot but I came out in the third set bouncing around.”
She faces Belarus’ Victoria Azarenka next, after the former world No.1 whistled past Daria Gavrilova 6-1, 6-2.
Elsewhere, the 2000 and 2001 champion, Venus Williams defeated Italy’s Camilia Giorgi 6-4, 7-5 to set up a blockbuster showdown with sister, Serena in the third round. Serena, who’s chasing a seventh US Open title made light work of Carina Witthoft 6-2, 6-2.
The Williams’ sisters matchup will be the earliest they’ve faced each other at a Grand Slam tournament in 20 years. Serena leads Venus 17-12 overall and 15-10 in Grand Slams.
Also, Ukrainian seventh seed Elina Svitolina advanced with a 6-2 6-3 win over Germany’s Tatjana Maria, while former world No.1 Garbine Muguruza failed to reach the third round as she beaten 3-6, 6-4, 6-4 by Karolina Muchova.