Ryan Harrison wasted the chance to claim a second shock US Open victory after failing to take three match points against Sergiy Stakhovsky.
American Harrison, 18, who beat 15th seed Ivan Ljubicic in the opening round, was 6-3 ahead in the fifth-set tie-break but lost the next five points in succession - one of them by crucially serving a double fault - as Stakhovsky held on for a 6-3 5-7 3-6 6-3 7-6 (8/6) victory.
"I just got a little bit tight when I needed to come through," admitted Harrison, who has been tipped by John McEnroe to eventually become one of the top 10 players in the world.
"It was incredibly fun, the first time I've played in the main draw at the US Open was two days ago and to have a crowd like that behind me was incredible.
"I'm obviously not the happiest person in the world right now, but looking back it was a great experience."
There was better news for the home crowd with John Isner, winner of the longest match in history at Wimbledon earlier this year, reaching the third round with a four-set win over Switzerland's Marco Chiudinelli.
Isner hammered down 24 aces on his way to a 6-3 3-6 7-6 (9/7) 6-4 win in just under three hours on Louis Armstrong Court.
Earlier in the day, unseeded Frenchman Michael Llodra today continued his superb form by also advancing to the last 32.
Llodra knocked out Wimbledon finalist and seventh seed Tomas Berdych in straight sets in the opening round and enjoyed a similarly comfortable win against Romania's Victor Hanescu.
The 30-year-old, who had lost 22 of his previous 36 first-round matches in grand slams, won 7-6 (7/2) 6-4 6-2 to set up a clash with Spain's Tommy Robredo.
Robredo had won the first set of his match against France's Julien Benneteau 6-4 and was in a second-set tie-break when Benneteau was forced to retire hurt.
The 28-year-old looked to injure his left wrist while playing a double-handed backhand, the innocuous incident appearing worryingly similar to the problem suffered by Britain's Andy Murray in Hamburg in 2007.
