In his first match since returning from a four-month doping ban, Marin Cilic beat qualifier Igor Sijsling 5-7, 6-1, 6-4 Monday to reach the second round of the Paris Masters.
The Croatian served 22 aces and hit 42 winners to only 17 for Sijsling.
Cilic tested positive for a banned stimulant in May but claimed he had not intended to ingest it in a glucose tablet bought at a pharmacy.
Feliciano Lopez of Spain, Lukas Rosol of the Czech Republic, Dutch qualifier Robin Haase and Colombian qualifier Santiago Giraldo also advanced to the next round.
Lopez outlasted Bernard Tomic 6-4, 6-7 (4), 7-6 (1). The Spaniard failed to serve out the match at 5-4 in the second set but he recovered in the tiebreaker of the third set by winning the last six points.