Seeds Denis Istomin and Tatsuma Ito notched opening-round victories Monday at the Kremlin Cup tennis event.
The sixth-seeded Istomin, of Uzbekistan, wrapped 12 aces before overcoming speedy German Bjorn Phau 5-7, 7-5, 6-1, while the eighth-seeded Ito, of Japan, held off Spaniard Roberto Bautista-Agut 6-3, 1-6, 6-2 indoors at Olympic Stadium.
Also on Day 1, Czech Lukas Rosol smacked 11 aces in topping Spaniard Daniel Gimeno-Traver 7-6 (11-9), 7-6 (7-2) and Tunisian Malek Jaziri cruised past American Rajeev Ram 6-3, 6-1.
The top seeds here are Ukrainian Alexandr Dolgopolov and Italian Andreas Seppi.
Janko Tipsarevic, who is not defending his title this week, beat 2010 champion Viktor Troicki in last year's all-Serbian Moscow finale.
This week's champion will take home $121,520.