Jo-Wilfried Tsonga claimed his first victory since February to knock Guido Pella out of the European Open, while defending champion Damir Dzumhur suffered a first-round exit at the Kremlin Cup.
Tsonga was beaten by Peter Gojowczyk at the Moselle Open last month in the first match of his comeback from knee surgery, but was back in business with a 7-5 5-7 7-6 (7-5) victory in Antwerp on Tuesday.
The Frenchman won the tournament in Belgium last year, but has not added to his tally since, enduring a frustrating spell off the circuit due to injury.
Tsonga will face compatriot Gael Monfils in what should be an entertaining second-round encounter after the flamboyant sixth seed eased past wildcard Ruben Bemelmans 6-0 6-3.
Gilles Simon was another French player who moved into the last 16 at the expense of Sergiy Stakhovsky on a day which saw eighth seed Robin Haase bow out with a straight-sets defeat to qualifier Ilya Ivashka.
Sixth seed Dzumhur's reign as champion in Moscow was ended by Egor Gerasimov, the world number 217 from Belarus pulling off a 6-1 6-7 (5-7) 6-2 upset.
Nick Kyrgios responded to his first-round exit at the Shanghai Masters by defeating Andrey Rublev 6-3 4-6 6-4, but eighth seed Martin Klizan went down 6-1 7-6 (8-6) to Andreas Seppi.
Benoit Paire, Dusan Lajovic, Evgeny Donskoy, Ricardas Berankis and Mirza Basic also negotiated their way into the second round.
Fifth seed Lucas Pouille made an early exit in the Stockholm Open, losing 6-4 6-4 to Tennys Sandgren.
Fernando Verdasco and Hyeon Chung had no such trouble, beating Matthew Ebden and Taylor Fritz respectively in straight sets.