Novak Djokovic rued a "horrible" performance as he crashed out of the Monte-Carlo Masters in his opening match.

The fifth-ranked Djokovic struggled to find his rhythm in a 6-3, 6-4 loss to Chilean Alejandro Tabilo in the second round on Wednesday, making an inauspicious start to his clay season.

Djokovic, 37, went into the tournament hampered by an eye infection that has been troubling him since the semi-finals in Miami at the end of March and admitting that he did not have "very high" expectations for Monte Carlo.

As it transpired a sluggish performance meant that Tabilo, who also beat Djokovic on clay in last year's Italian Open in Rome, faced few difficulties in claiming a rare 2-0 head-to-head record against the 24-time Grand Slam winner.

"It was actually more like the worst day [at the office]," said Djokovic.

"I was hoping it was not going to happen, but it was quite a high probability I'm going to play this way.

"Just horrible. Horrible feeling to play this way, and just sorry for all the people that have to witness this."

The Serb, who is chasing his 100th ATP title, has not won a tournament since taking gold at last year's Paris Olympics.

Djokovic brushed off any fitness concerns and said his main focus for the clay season was the French Open.

He is set to play in Madrid later this month for the first time since 2022.

"I expected myself at least to have put a decent performance. Not like this. It was horrible," said Djokovic, who has only once reached the semi-finals in Monte Carlo since the last of his two titles in the principality in 2015.

"I did not have high expectations, really. I knew I'm gonna have a tough opponent and I knew I'm gonna probably play pretty bad.

"But this bad, I didn't expect."

Tabilo, ranked 32 in the world, will face Bulgarian Grigor Dimitrov in the last 16.

"It has been a tough year, so a little bit of the nerves were there," said Tabilo, who earned consecutive tour-level wins for the first time since August.

"It was an unreal match." (AFP)