Istomin impresses against Isner
Third seed John Isner was bundled out of the US National Indoor Championships in Memphis, with Denis Istomin sealing a straight-sets victory.
Isner was beaten 6-4 6-3 in the first round 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(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.
In the women's side of the competition, Lucie Hradecka was the only seed to exit.
The Czech player, placed fifth in the draw, was short of her best in a 6-3 6-4 defeat at the hands of Claire Feuerstein.
Elsewhere, the chances of home success took a battering as four Americans crashed out.
Third seed Sabine Lisicki got the ball rolling by seeing off Madison Keys 7-5 6-3, Magdalena Rybarikova added the scalp of Lauren Davis 7-6(2) 6-2 and Melanie Oudin fell 4-6 6-3 3-6 to Andrea Hlavackova.
The remaining match was an all-American affair, Jamie Hampton progressing at the expense of Coco Vandeweghe.