Former world number 17 Cristian Garin was beaten 6-4 7-5 by Federico Coria in the first round of the Austrian Open in Kitzbuhel, while Matteo Berrettini and defending champion Casper Ruud withdrew from the tournament.
2017 runner-up Joao Sousa cruised past Vit Kopriva 6-1 7-5 and Jurij Rodionov set up a Round of 16 meeting with third seed Roberto Bautista Agut with a straight-sets victory over Hernan Casanova.
Dominic Thiem, who won the 2019 edition of the competition, will face Alexander Shevchenko tomorrow while Richard Gasquet will take on Sebastian Ofner.
2016 Croatia Open winner Fabio Fognini will not be regaining his title in Umag this year, after the seventh seed was knocked out by Colombian Daniel Galan in a 3-6 7-5 3-6 defeat.
Galan will play Giulio Zeppieri in the next round, who came from one set down to overcome world number 90 Pedro Cachin 3-6 6-1 6-4.
Fifth seed Alex Molcan plays his first game tomorrow against Duje Adjukovic, and sixth seed Daniel Altmaier will take on French 23-year-old Corentin Moutet.