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.
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.