Cilic hadn't played since Wimbledon due to a suspension after he tested positive for a banned substance. He said he inadvertently took the substance and the International Court of Arbitration last week cut an original nine-month ban to four months.
Cilic returned to play with a 5-7, 6-1, 6-4 victory over Igor Sijsling. Cilic did have some rust as shown by six double faults and a 47 percent figure on landing first serves. But he also had 21 aces and only lost his serve once.
He heads into the second round against world No. 5 Juan Martin del Potro who has won 15 of his last 16 matches and two tournaments since the U.S. Open.
Qualifiers Santiago Giraldo and Robin Haase also worked their way into the second round. Giraldo stopped Adrian Mannarino 6-3, 2-6, 6-4 by posting the only break of the third set. Haase defeated Denis Istomin 7-6 (10-8), 6-3 by saving two of the three break points he faced.
Also Monday, Fernando Verdasco edged by Ernests Gulbis 7-6 (7-3), 7-6 (7-5) in nearly 2 hours; Kei Nishikori took out Julien Benneteau 6-4, 6-2; and Philipp Kohlschreiber got past Andreas Seppi 6-3, 3-6, 6-4. Feliciano Lopez was a 6-4, 6-7 (4-7), 7-6 (7-1) winner over Bernard Tomic in the day's longest match -- 2 hours, 22 minutes -- and Pierre-Hugues Herbert capped Monday's play with a 6-2, 6-2 romp past Benoit Paire in 59 minutes.