(CNN) -- Petra Kvitova made a convincing start to her bid for back-to-back grand slams with the loss of just one game in seeing off Kristina Mladenovic of France Tuesday at Flushing Meadows.
The Wimbledon champion has come into the U.S. Open after a morale boosting victory in the preceding New Haven tournament and again looked impressive.
The third-seeded Czech broke her 73rd-ranked opponent five times in a one-sided contest to earn a second round clash with compatriot Petra Cetkovska.
But there was a upset defeat for Australian Open finalist Dominika Cibulkova, who was stunned by 15-year-old American Catherine Bellis 6-1 4-6 6-4.
Bellis becomes the youngest winner at the U.S. Open since Anna Kournikova in 1996 as she beat the 12th seed, who has endured a miserable summer on the hard courts.
Other seeds fared better led by by seventh ranked Eugenie Bouchard of Canada, beaten by Kvitova in the Wimbledon final.
Bouchard has struggled since her heroics at SW19, but eased past Olga Govortsova of Belarus on the Louis Armstrong court with a 6-2 6-1 victory.
Govortsov had three break points at 2-2 in the first set but could not convert and won just a single game thereafter.
Bouchard hit 19 winners overall and few unforced errors to get another grand slam campaign rolling.
"I'm happy to get a match under my belt and want to keep it rolling this week," said Bouchard. "I love playing the grand slams and just want to raise my level at the biggest stages and the biggest matches," she told the official U.S. Open website.
Former world number one Ana Ivanovic, seeded eighth, opened her campaign with a 6-3 6-0 win over American Alison Riske.
The Serbian has won three titles in 2014 and beat top ranked Serena Williams in the fourth round of the Australian Open on the way to the last eight, her career transformed last year after a form slump.
"Last year has been amazing change for me. I learned a lot about myself, about my goals, who I am as a person and who I want to be.
"This is what I had to discover -- what was my goal," she told gathered reporters.
But 20th seed Svetlana Kuznetsova made an early exit to Marina Erakovic of New Zealand on the 10th anniversary of the Russian's 2004 triumph at Flushing Meadows.
Kuznetsova was edged out 3-6 6-2 7-6 in two hours 19 minutes.
Williams, top seed in the women's tournament and Swiss maestro Roger Federer were opening their campaigns in the night session later Tuesday.