Stan Wawrinka's ATP Tour return at the Monte-Carlo Masters ended in defeat, while Jannik Sinner came through a tense encounter with Borna Coric. 

The former world number three made his comeback after more than a year out with a left foot injury that required two surgeries but fell to a 3-6 7-5 6-2 defeat to Alexander Bublik in the first round. 

Wawrinka, who entered the tournament as a wildcard having slipped to 236 in the world rankings, came from a break down to take the opening set but fatigue eventually set in and he was eliminated after two hours and seven minutes. 

"I think the body's getting much better," said Wawrinka, who lost in straight sets to Elias Ymer at a Challenger tournament in Marbella two weeks ago. 

"I'm still far away from where I want to be, but I think I'm [going in] the right direction. I think today was a positive match. It was a tough loss, of course, but I'm happy with the way I was playing today. 

"I was playing better, feeling better on the court physically. I spent a lot of mental energy to focus, to stay there as it was tough at the end. But I'm happy with what I have done."

Ninth seed Sinner was taken the distance by Coric before completing a 6-3 2-6 6-3 victory to advance to the second round. 

Sinner took a medical timeout in the second set while he dealt with some apparent abdominal pain, but he was able to battle back and take the win. 

Diego Schwartzman needed over three hours to come from behind and defeat Karen Khachanov 6-7 (5-7) 6-3 6-3, while his fellow Argentine Federico Delbonis set up a clash with second seed Alexander Zverev by besting Jaume Munar 6-4 3-6 6-4. 

Reigning champion Stefanos Tsitsipas faces a meeting with Fabio Fognini in the second round after the Italian overcame Arthur Rinderknech 7-5 4-6 6-3.  

There were also wins for Hubert Hurkacz, Pablo Carreno Busta, Marin Cilic, Alex de Minaur, Albert Ramos-Vinolas and Sebastian Korda.