Istomin saved both break points in faced in a 6-1, 6-2 rout of eighth-seeded Martin Klizan. Istomin won more points (50-49) off Klizan's serve while posting four breaks over seven games receiving serve.
Seventh-seeded Jurgen Melzer survived a tough 2-6, 6-4, 6-4 battle against Denis Kudla in his first-round match. Melzer lost his serve three times in the first set but only saw two break points -- saving both -- the rest of the way.
Wild-card entrant Lleyton Hewitt, entering his 16th year on the ATP tour, defeated Igor Kunitsyn, who was replacing Radek Stepanek in the draw. Stepanek withdrew due to an eye infection. Hewitt, 31, beat Kunitsyn 6-3, 4-6, 6-2, losing 19 points on serve in the match.
Also Tuesday, qualifier John Millman beat Tatsuma Ito 6-4, 6-1; Tommy Robredo got past Ryan Harrison 6-4, 7-6 (7-4); Alejandro Falla stopped Jesse Levine 6-1, 7-6 (10-8); David Goffin raced past Matthew Ebden 6-2, 6-2; and Grigor Dimitrov eliminated Brian Baker 6-3, 7-6 (10-8).
Celebrity Couples of 2014 [PHOTOS]