Bellis, ranked at a lowly 1,208 and aged just 15, knocked out Australian Open runner-up Dominika Cibulkova 6-1, 4-6, 6-4 to become the youngest player to win a match at the US Open since Anna Kournikova in 1996.
“I went into the match thinking it was going to be such a great experience, but I never thought I would come out on top winning,” said Bellis who, as an amateur, had to pass up the $60,000 prize money to avoid jeopardising a college sports career.
Coric, the 17-year-old world number 204 who was junior champion in 2013, also made a stunning grand slam debut 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.
“It’s an amazing feeling,” said qualifier Coric. “I said to myself, ‘If I achieve that, that’s going to be perfect’.”
Meanwhile Federer, playing in his 60th successive Grand Slam and bidding to become the oldest major winner in over 40 years, defeated Australia’s Marinko Matosevic 6-3, 6-4, 7-6 (7/4) to register his 23rd win in 24 night matches in New York.
“It was a bit more difficult than I thought it was going to be in the third set. Marinko has a big game,” said second-seeded Federer.
Women’s world number one Serena, the double defending champion who is also seeking a sixth title, was equally untroubled, defeating 18-year-old compatriot Taylor Townsend 6-3, 6-1 in just 55 minutes.