The former U.S. Open champion pulled her game together just in time to beat Tsvetana Pironkova of Bulgaria 7-6 6-2, but for the second match in a row she was well short of her best.
"I was feeling not bad there, but it was a very weird match, not very consistent," the Russian told reporters.
"I didn't start well, definitely, and I was messing it up, and she was playing pretty good.
"Then I was getting a bit tighter and I still didn't play my game. But when I was down 5-2, 5-3, I felt I'm just not doing the things. It's not easy to get the rhythm." Pironkova, ranked 92 places behind her opponent at 94th in the world, had a set point in the ninth game but the Russian hit back.
With world number two Kuznetsova making a host of unforced errors, Pironkova raced into a 5-2 lead and held a set point on her own serve at 5-3.
But Kuznetsova found her form to win the tiebreak 7-0 and eased through the second set to line up a clash with Polish 29th seed Agnieszka Radwanska.
"I played better (in the second set)," she said. "I still was not happy with the first set, but I couldn't change anything so I just did better in the second.".