Rafael Nadal, 4/1 with bet365 to successfully defend his US Open title, failed to impress in his first-round victory over Andrey Golubev.
The Spaniard was behind in all three sets, but eventually prevailed 6-3 7-6 7-5.
Meanwhile, world number one Novak Djokovic, 7/5 to emerge victorious in New York, was 6-0 5-1 ahead in his first round clash against Conor Niland when the Irishman was forced to retire because of illness.
In the women’s tournament, British number one Elena Baltacha reached the second round when her opponent, American wildcard Jamie Hampton, retired after collapsing.
Serena Williams eased past Bojana Jovanovski 6-1 6-1 in less than an hour.