By Steve Ginsburg
The 2008 U.S. Open finalist received medical attention several times during the match but still managed to advance with a 6-3 6-4 triumph at the National Tennis Center.
"I hurt it in the first set," said Jankovic. "I felt a little restricted when I was hitting my serves and especially when I had to bend down when I was waiting to return her serves."
"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. I think I will be OK."
Jankovic, 26, said there were times against Dokic she would "be on a roll and control the whole game."
"But then I had some problems, and then I would kind of stop and I wouldn't move as much," added the Serbian. "Then I started double faulting because I couldn't push off."
Jankovic played conservatively and was a spectator to Dokic's self-destructive play.
Dokic, playing in just her second U.S. Open main draw in seven years, recorded an early service break but unraveled midway through the first set and never recovered.
The Australian's serve played a big role in the loss as the 2000 Wimbledon semi-finalist committed 15 double faults while successfully landing just 48 percent of her first serves.
"Obviously, my serve let me down," she said. "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."
"We're all injured pretty much," she said. "I'm serving at 50 percent. We all have something. We all call the trainer at some point for our back. We can wake up with it.
"I don't really think it affected her too much."
(Editing by Frank Pingue)