The third-seeded Sharapova was tested mightily in a 3-6, 7-5, 6-3 come-from- behind victory over Britain's Heather Watson at Ashe Stadium. The tall Russian needed 2 hours, 34 minutes to reach the round of 64.
The promising 19-year-old Watson was up a set and then broke Sharapova to open the second, but the Russian star broke right back to mount her comeback on Day 1.
A sloppy Sharapova tallied eight double faults and a whopping 58 unforced errors, but also struck 32 more winners (41-9) than the young Watson.
The 24-year-old Sharapova has now won her last six matches overall, including a hardcourt title in Cincinnati two weeks ago.
Sharapova is a former world No. 1 and three-time Grand Slam champion, including a U.S. Open title back in 2006. She was this year's Wimbledon runner-up to Kvitova.
The second-seeded 2010 U.S. Open and Wimbledon runner-up Zvonareva zipped past France's Stephanie Foretz Gacon 6-3, 6-0 at Armstrong Stadium.
The Russian Zvonareva was dismantled by Kim Clijsters, 6-2, 6-1, in last year's lopsided U.S. Open finale.
Meanwhile, 22-year-old Romanian Alexandra Dulgheru, ranked 48th in the world, stunned the fifth-seeded Kvitova 7-6 (7-3), 6-3 at the USTA Billie Jean King National Tennis Center, which was in terrific shape after weathering Hurricane Irene over the weekend. Kvitova piled up 52 unforced errors en route to her early exit.
Since upending Sharapova in last month's Wimbledon finale, Kvitova has gone just 2-3 overall.
Thirteenth-seeded Chinese Peng Shuai doused American Varvara Lepchenko 6-3, 6-4, while 19th-seeded Julia Goerges leveled fellow German Kristina Barrois 6-3, 6-2 and 27th-seeded Czech Lucie Safarova overcame Slovakian Magdalena Rybarikova 2-6, 6-3, 6-2.
Sixteen-year-old Madison Keys dismissed 37-year-old Jill Craybas 6-2, 6-4 in an all-Ammerican affair.
"This is my first time in the main draw here, and obviously it was a good first day," said the big-hitting Keys.
The top seed here is last week's New Haven titlist Caroline Wozniacki, the 2009 U.S. Open runner-up to Clijsters, who had won the last two titles here in Flushing but is missing this year's fortnight because of injury.
This year's U.S. Open singles champ will pocket at least $1.8 million, and U.S. Open Series winner Serena Williams, seeded 28th, has a shot at earning a record $2.8 million in the Big Apple. The three-time U.S. Open titlist Serena has won her last 12 matches overall and is considered one of the favorites in New York.