Women's world number one Simona Halep of Romania on Monday was knocked out of the US Open in straight sets on a day that saw men's veterans and former winners Andy Murray and Stan Wawrinka through to the next round.
Halep was beaten 6-2, 6-4 in the opening round of the grand slam tournament in New York by world number 44 Kaia Kanepi. The 33-year-old Estonian upset the French Open champion by blasting 26 winners compared with nine for Halep.
Kanepi also broke Halep's serve five times as she took her second career win over a world number one.
Murray, the 2012 US Open winner, fought back from a set down to defeat James Duckworth of Australia 6-7 (7-5), 6-3, 7-5, 6-3. It was the 31-year-old's first grand slam appearance since last year's Wimbledon, where he lost in the quarter-finals.
Murray had hip surgery in January and pulled out of this year's Wimbledon the day before it started. He and Duckworth played in the new Louis Armstrong Stadium at the US Open at Flushing Meadows, New York.
"It's like a new beginning," Murray said in a court-side interview with ESPN, acknowledging that he lost a lot of matches in the old stadium. "It was beautiful - a great atmosphere for the first day of the tournament."
Wawrinka, the 2016 winner, defeated eighth-seeded Grigor Dimitrov of Bulgaria 6-3, 6-2, 7-5. The Swiss has been on the comeback trail after knee surgery earlier this year.
Rafael Nadal begins the defence of his title later Monday. Novak Djokovic and Roger Federer lead a pack of determined challengers trying to stop Nadal from becoming the first man to repeat as champion in New York in a decade.
Nadal, world number one and three-time champion in New York, takes on fellow Spaniard David Ferrer in an evening match on Monday. Nadal holds a 24-6 record against Ferrer and comes into the Open on the strength of a victory in the Rogers Cup in Toronto, a hard court tune-up ahead of the New York slam.
World number two Federer, at 37 the oldest player in the field, is on the hunt for his sixth US Open title. If the number two seed wins and Nadal fails to make the semi-finals, he'll not only pocket 3.8 million dollars, he'll steal away the number-one ranking.
Federer and Western and Southern Open champion Djokovic, seeded sixth, play their opening matches on Tuesday. Despite high expectations for Federer and Nadal, Djokovic has been tapped as the favourite to win his third US Open.
Defending women's champion Sloane Stephens meanwhile takes on Evgeniya Rodina of Russia. She faces further stiff competition from Wimbledon champion Angelique Kerber and 23-time grand slam winner and fellow American Serena Williams.
In other matches in the women's draw Monday, Williams will be on the court for her first match of the tournament against Magda Linette of Poland.