Kafelnikov defeated Vacek of the Czech Republic, 7-6 (7-4), 6-4, improving to 15-4 all-time in head-to-head matchups. The two have won three Grand Slam doubles titles and numerous smaller events.
The 27-year-old Kafelnikov reached the quarterfinals here last year to start a season in which he captured two titles and finished ranked No. 4 in the world.
Vacek came back from injuries in 2001, compiling a 2-7 record. He fell to 1-4 lifetime in Doha.
No. 8 Felix Mantilla of Spain, the only other seeded player in action Monday, thrashed Italian qualifier Cristiano Carrati, 6-1, 6-1. Mantilla claimed his lone title last year in Sicily and was a finalist at Estoril.
Also, Bohdan Ulihrach of the Czech Republic dispatched Galo Blanco, 6-2, 6-2; Jonas Bjorkman of Sweden overcame Jan Vacek of the Czech Republic, 6-4, 6-7 (2-7), 6-3; and Oleg Ogorodov of Bulgaria routed wild card Nasser Al-Khulaifi of Qatar, 6-1, 6-2.
Moroccan Younes El Aynaoui outplayed Frenchman Cedric Pioline, 7-6 (7-2), 6-4; Nikolay Davydenko won the battle of young Russians against Mikhail Youzhny, 6-4, 6-2, and Armenia's Sargis Sargsian rolled past Argentina's Franco Squillari, 6-0, 6-3.