Teenagers Bellis, Coric gatecrash US Open
Eugenie Bouchard of Canada tosses the ball as she serves to Olga Govortsova of Belarus during the 2014 US Open women's singles match at the USTA Billie Jean King National Tennis Center August 26, 2014 in New York - by Kena Betancur
Bellis, just 15, caused the biggest upset when she knocked out Australian Open runner-up, Dominika Cibulkova, the 12th seed, 6-1, 4-6, 6-4 to become the youngest player to win a match at the US Open since Anna Kournikova in 1996.
Playing just her 13th pro-level match, the American teenager won a wildcard into the US Open by winning the US under-18 championships.
The home-schooled teenager from the wine-growing Napa Valley in northern California was making her WTA Tour debut and before Tuesday had never met a player ranked inside the top 100.
Coric, 17, who was the junior champion in 2013 and came through qualifying this year, celebrated his first Grand Slam match with a convincing 6-4, 6-1, 6-2 win over 29th-seeded Czech Lukas Rosol, the man who dumped Rafael Nadal out of Wimbledon two years ago.
The upset put Coric into a second-round clash with history-making Victor Estrella Burgos, the Dominican Republic's first Grand Slam participant who is making his US Open debut at 34.
"It's an amazing feeling," said Coric, who arrived in New York with the goal of making it into the main draw. "I said to myself, 'If I achieve that, that's going to be perfect'."
Wimbledon champion Petra Kvitova breezed into the second round with a 6-1, 6-0 rout of French number 73 Kristina Mladenovic.
The third-seeded Czech didn't surrender a service break in the 54-minute contest, breaking Mladenovic five times.
Canadian seventh seed Eugenie Bouchard, the Wimbledon runner-up, eased past Olga Govortsova of Belarus 6-2, 6-1, slamming the brakes on her post-All England Club final slump which had brought her just one win coming into New York.
Bouchard is one of four Canadians in the main draw this year, the most since 1989 and is aiming to keep up her record of having made at least the semi-finals at all the majors in 2014.
The sport's new poster girl said she had learned from her Wimbledon final hammering at the hands of Kvitova.
"It was an experience I'll never forget. I have happy memories from that day, as well, even though I lost. I felt I could have done a few things better. But again, my opponent definitely outplayed me," she said.
- Federer, Serena ready -
Former French Open champion Ana Ivanovic, the eighth seed, eased past Alison Riske of the United States, 6-3, 6-0 in a tie which featured eight breaks of serve.
It was a performance which suggested the Serb is getting back close to her best in a year which has seen her beat Serena Williams in the Australian Open fourth round, claim three titles and return to the world's top 10 for the first time in five years.
Later Tuesday, five-time champions and 17-time major winners Roger Federer and Serena Williams get their 2014 campaigns under way on Arthur Ashe Stadium.
Federer, seemingly down and out in New York 12 months ago after suffering his earliest loss at the tournament for a decade, begins his 15th US Open as one of the favourites.
The 33-year-old Swiss, bidding to become the oldest major winner in more than 40 years, faces explosive Australian Marinko Matosevic who he beat in their only other previous meeting at Brisbane earlier this year.
Playing in a record 60th consecutive major, Federer boasts a 22-1 record in New York night sessions.
World number one Williams failed to make it past the fourth round at the Australian Open, French Open and Wimbledon this year.
The American is bidding to join Chris Evert and Martina Navratilova as an 18-time Grand Slam singles champion and she starts her 2014 tournament against compatriot Taylor Townsend, a tough, 18-year-old left-hander who has lost in qualifying in the last two years.
Australia's Samantha Stosur, the 2011 champion, went through with a 6-1, 6-4 win over Lauren Davies of the United States, firmly erasing the nightmare of her 2013 first round exit to US teenager Victoria Duval.
However, another former champion, Svetlana Kuznetsova, the 2004 winner was dumped out 3-6, 6-2, 7-6 (7/3) by New Zealand's Marina Erakovic who won her first US Open match at the fifth time of asking.
China's Zhang Shuai can only dreamke of the success achieved by the likes of Williams, Ivanovic and Stosur.
The 32nd seed lost 6-1, 6-2 to Germany's Mona Barthel leaving her with a 0-12 career record at the Grand Slams.
There was a minor psychological victory for 32-year-old Italian Paolo Lorenzi whose win against Japanese qualifier Yoshihito Nishioka was his first at the Grand Slam level after 13 losses.