Damir Dzumhur started the defence of his Antalya Open title with a straight-sets defeat of Matthew Ebden on Monday.
Dzumhur claimed his maiden ATP Tour grass-court title in Turkey last year and the fifth seed is eyeing a repeat after seeing off Australian Ebden 6-4 7-5 a week before Wimbledon starts.
Bernard Tomic had a much better day than his compatriot Ebden, beating seventh seed Andreas Seppi 4-6 6-4 6-4.
Ugo Humbert, the sixth seed, advanced with a 6-3 7-5 victory over Federico Delbonis, while Roberto Carballes Baena, Viktor Troicki, wildcard Altug Celikbilek prevailed.
Bradley Klahn, Prajnesh Gunneswaran and Peter Gojowczyk also advanced to round two.
How about a for defending champ @DzumhurDamir breaking Matthew Ebden's serve three times to move on @antalyaopen— ATP Tour (@ATP_Tour) June 24, 2019
Marco Cecchinato was unable to end his poor run of form at the Nature Valley International, Hubert Hurkacz toppling the seventh seed 6-4 6-4.
Steve Johnson, the champion in this event three years ago, saw off fellow American Reilly Opelka 7-6 (7-4) 6-3.
Sam Querrey and Taylor Fritz also made it through and Fernando Verdasco saw off John Millman.
Play was suspended due to rain with Cameron Norrie leading Jeremy Chardy 3-0 in the first set and the poor weather meant Nicolas Jarry and Pablo Cuevas did not take to the court.