Sharapova underwent shoulder surgery in 2008 and has been prone to double-faults, but in the final set she had no trouble with her serve — or anything else. She won 21 of the last 27 points and finished with just 11 unforced errors.
Sharapova said she didn't make any major changes down the stretch.
"We were playing with the same balls; I played with the same racket," she said. "I just started doing things a little bit better."
Pironkova, ranked 38th, beat Venus Williams at Wimbledon each of the past two years,
"If she played on grass 365 days a year, she'd be top five probably," Sharapova said. "She has the perfect game for it."
But Sharapova's at her best in winner-take-all sets. She improved her record in three-set matches to 9-0 this year and 21-1 since the beginning of 2011.
She has won 14 consecutive matches, including the French Open this month to complete a career Grand Slam.
While Sharapova battled an erratic serve, with eight aces and 10 double-faults, four-time champion Serena Williams had no such trouble. She won 27 of 28 points on her first serve, including 10 aces, and never faced a break point. Czink twice whiffed on returns.
"I love my serve," Williams said, "and I love feeling good when I serve."
The sixth-seeded Williams could meet Sharapova in the final next week. A 17-year-old Sharapova defeated Williams for the Wimbledon title in 2004.
Roddick advanced to the third round at a Grand Slam tournament for the first time in 2012 when he beat Bjorn Phau 6-3, 7-6 (1), 6-3. Roddick is seeded only 30th and fended off questions in recent months about retirement before he won his fifth grass-court title last week as a wild card at Eastbourne.