After losing a second-straight opening match and three in a row overall, Novak Djokovic admits he is facing a "new reality" in his two decades of pro tennis.

Djokovic's public coming-to-terms with his rare losing streak came after he fell in straight sets to Italian Matteo Arnaldi in his first match of the Madrid Open on Saturday.

The 37-year-old came to Spain after also losing his opener to Alejandro Tabilo at the Monte Carlo Masters two weeks ago and, before that, the Miami Open final.

"I was hoping I can play one more match than I played in Monte Carlo. It's kind of a new reality for me, I have to say, trying to win a match or two, not really thinking about getting far in the tournament," Djokovic said.

The struggles by the record winner of 24 grand slam men's singles titles coincide with the start of the clay-court swing, which culminates in the French Open next month.

"It's a completely different feeling from what I had in 20-plus years of professional tennis," he said. "It's a challenge for me mentally to really face these kinds of sensations on the court, going out early now, regularly, in tournaments."

Arnaldi won 6-3 6-4, delaying Djokovic's search for a career 100th title, the Serb undermined by 32 unforced errors to his opponent's 18, with his serve broken three times.

"He's my idol, he's always been," Arnaldi said of Djokovic. "To play him at a stage like this was already a victory for me. He's not at his best right now, so I came on court to try to play my best tennis and win - and it happened."

Djokovic is still seeking his first title of the season after winning his 99th title last August at the Paris Olympics.

He has lost four finals since then. The only two players to reach the 100-title milestone are Jimmy Connors (109) and Roger Federer (103).