Jelena Jankovic saw off Jelena Dokic 6-3 6-4 to reach the third round of the US Open - but victory may have come at a price for the 11th seed.
Jankovic needed medical treatment several times during Thursday's opening match on Louis Armstrong Stadium after suffering a back injury.
The 2008 finalist at Flushing Meadows was forced to play conservatively due to the problem, though Dokic helped her out with a plethora of unforced errors.
The Australian, in the main draw in New York for just the second time in seven years, was particularly poor on her own serve, sending down 15 double faults.
She had actually managed to gain an early break of serve but then unravelled midway through the opening set. In all, she was broken on nine occasions.
"Obviously, my serve let me down," Dokic said afterwards. "It's not a surprise. I've had a shoulder injury for six weeks. I've hardly served, even in practice.
"I felt like I was playing well off the ground, winning most of the points. If I didn't have the double faults, the score would probably be the other way around."
Jankovic will next face Anastasia Pavlyuchenkova after the Russian battled past Petra Martic of Croatia 6-4 2-6 6-4.
"I think I will be okay," the 26-year-old stated.
"I have a day off tomorrow and I will just try to receive some treatment and feel the best as possible for my next match."
Meanwhile, Jankovic's fellow Serbian Ana Ivanovic didn't even have to hit a ball to reach round three, as her opponent Petra Cetkovska was forced to withdraw from the match.
Seventh seed Francesca Schiavone enjoyed a 6-1 6-1 success over Mirjana Lucic of Croatia, while another Italian, Roberta Vinci, defeated France's Alize Cornet 6-2 6-3.
Life was a lot tougher for the 10th-seeded Andrea Petkovic though, the German having to come from a set down to see off Zheng Jie of China 3-6 6-3 6-3.