The world ranked No. 90 broke Thiem's serve five times in what was a surprisingly lackluster display from a man who has won eight ATP titles on clay.

Thiem served five double faults in a tournament he won in 2017.

"He played a bit worse than normally I think, to be honest," Djere said. "But I had a great day. I felt the ball really well, hitting well from the baseline and then attacking well when it was time for that."

"The biggest win in my career so I'm really happy right now."

In another upset, third seed Marco Cecchinato was beaten 7-5, 7-6(1) by Slovenian Aljaz Bedene.

Cecchinato was on a high after winning the Argentina Open on Sunday but he never hit the same heights against the unseeded Bedene.