Federico Delbonis and Laslo Djere crashed out of the Generali Open in the first round on Tuesday.
Fifth seed Delbonis and sixth seed Djere were the highest-ranked players in action on day two, but both fell to surprise defeats.
Delbonis, a recent semi-finalist at the Hamburg European Open, was convincingly beaten 6-2 6-4 by Arthur Rinderknech.
Frenchman Rinderknech fired down 10 aces and was only broken once in the contest.
— ATP Tour (@atptour) July 27, 2021
Djere, meanwhile, put up more of a fight but ultimately succumbed to Daniel Altmaier, who won 4-6 6-3 6-3 in a battle lasting two hours and 10 minutes.
World number 50 Djere had also made the semi-finals in Hamburg and followed that up with another run to the last four at the Swiss Open Gstaad.
But his run of form came to an end as German Altmaier – who himself enjoyed a semi-final run in Croatia last week – booked a last-16 tie meeting with Marco Cecchinato after breaking Djere on six occasions.
Cecchinato had beaten Radu Albot in straight sets to reach the next round while qualifier Jozef Kovalik saw off Jaume Munar with a 6-4 6-4 victory.
The top four seeds, including number one Casper Ruud, will begin their campaigns at the ATP 250 event in Kitzbuhel on Wednesday.