Kubot came out on top of a 4-6, 6-3, 6-4 decision over Istomin in a match that took 2 1/2 hours. Kubot won four more points -- 102-98 -- over the course of the match but the difference for him was finishing off three breaks over the second and third sets.
That was the only upset in Wednesday's results but fourth-seeded Fabio Fognini needed to come from behind for a 4-6, 6-2, 6-3 win over Tobias Kamke. Fognini won 69 percent of the points on serve over the last two sets.
No. 3-seeded Martin Klizan topped Mikhail Elgin 6-4, 6-3 and eighth-seeded Jurgen Zopp was up 6-3, 5-3 when Andrey Kumantsov retired from the match.
Other results Wednesday as the first round wrapped saw Paolo Lorenzi stop Sergey Betov 1-6, 6-2, 6-2; Simone Bolelli edge Horacio Zeballos 7-6 (7-3), 7-5; Teymuraz Gabashvili rout Nikola Fidirko 6-2, 6-0, in 49 minutes; Sergiy Stakhovsky beat Ivan Nedelko 7-6 (7-2), 6-2; and Ricardas Berankis, who was up 6-2, 3-3, make the second round when Philipp Petzschner retired.