Third seed John Isner was bundled out of the US National Indoor Championships in Memphis at the first opportunity, with Denis Istomin sealing a straight-sets victory.
Isner was beaten 6-4 6-3 by his Uzbekistani opponent, ranked number 63 in the word.
There were three American winners on the day to make up for Isner's exit.
Fourth seed and 2010 champion Sam Querrey defeated Colombian Alejandro Falla 6-3 6-3, James Blake edged Florian Mayer 4-6 6-3 6-2 and Michael Russell was a 6-2 6-4 winner over Alex Bogomolov
Japan's Kei Nishikori, seeded fifth, defeated Illya Marchenko 6-4 7-5 to reach the second round safely and will be joined by Holland's Igor Sijsling, who recorded an impressive 6-4 7-6 (7/3) victory over Jurgen Melzer.
Feliciano Lopez was the final winner in the men's side of the draw, courtesy of a 4-6 6-3 6-4 result over Benjamin Becker.