Her game faltered in the second set, and she admits she lost focus, saving two set points before fighting back to win it 7-5.
"I was pretty good up until the end of the first set but in the second I was feeling a little cooled down," she said.
"When she broke me I felt a little stressed. That's the problem for me, I am always a little up and down.
"When I can focus on court I put pressure on opponents, but I need to focus better as the tournament goes on."
The former French Open champion will now play 27th seed Sorana Cirstea in the third round.