Keothavong's highest world ranking to date is 76
British number one Anne Keothavong won her first ever Grand Slam match away from Wimbledon with victory over Alexa Glatch at the US Open.
Keothavong qualified directly for the main draw after a run that has seen her rise to 87 in the world rankings.
And the 24-year-old Londoner took advantage on her Flushing Meadows debut, beating American qualifier Glatch 6-2 6-2.
Keothavong will play Italy's 25th seed Francesca Schiavone in round two.
Schiavone defeated Spain's Nuria Llagostera Vives 7-5 7-5.
Keothavong had little trouble in easing past an opponent 179 places lower than her in the rankings.
The Briton overcame a slight sign of nerves with a double fault on her first match point to seal it with an ace down the middle.
"I'm obviously pleased with the result," said Keothavong. "I thought l played a good solid match and am just pleased to be through to the next round.
"She's not to be underestimated, even though I'm ranked higher than her. She's a tricky opponent but I thought I handled her well.
"I feel I'm definitely on the right path; I'm moving forward and feeling confident, feeling good out there."