Novak Djokovic's 16-match Key Biscayne winning streak ended, and his struggle to come back from an elbow injury continued.
Djokovic lasted barely an hour at a tournament he has won six times, losing his opening match Friday in the Miami Open to Benoit Paire, 6-3, 6-4.
The defeat was Djokovic's third in a row. He returned from a six-month injury absence at the Australian Open and lost in the fourth round, and was upset two weeks ago at Indian Wells by Taro Daniel, a 109th-ranked qualifier.
"I'm trying, but it's not working," Djokovic said. "Obviously I'm not feeling great when I'm playing this way. Of course, I want to be able to play as well as I want. Just it's impossible at the moment. That's all."
Against the 47th-ranked Paire, Djokovic dropped serve four times, returned poorly and had difficulty anticipating his crafty opponent's drop shots.
"It happened very fast," Djokovic said. "I'm just, in general, trying everything I can. I'm not at the level that I used to be. I'm aware of that. I just have to obviously believe in myself, and hopefully, it will come."
In women's play, Naomi Osaka's breakthrough winning streak ended with a loss to No. 4-seeded Elina Svitolina 6-4, 6-2. Osaka said began feeling ill before the match but didn't want to retire after upsetting eight-time champion Serena Williams in the first round.
The 20-year-old Osaka is ranked a career-high 22nd and won her first career title last week at Indian Wells.
Three-time champion Venus Williams defeated Natalia Vikhlyantseva 7-5, 6-4. Juan Martin del Potro, playing for the first time since beating Roger Federer in last week's Indian Wells final, outlasted Robin Haase 6-4, 5-7, 6-2.
Djokovic sat out the last half of 2017 because of problems with his racket-swinging arm, saying it had been bothering him for more than a year. He has sidelined again after this year's Australian Open and said he had a "small medical intervention" on his elbow.
The 12-time Grand Slam champion didn't seem to favour it against Paire, but his shots lacked their usually snap and sometimes were awkwardly struck, including the last two on match point.
In the first set Djokovic served with a chance to reach 5-all, but from 40-0 he lost five consecutive points and the set. Another dismal stretch came when he was broken at love in the final game of the match.
When asked if he expects to regain his championship level, Djokovic said he didn't know. He was also noncommittal about his schedule for the upcoming clay season.
"I don't want to sit here and whine about my last couple of years," Djokovic said. "The truth is that it wasn't easy. Obviously, I compromised my game and the movement and everything because of the injury. I'm trying to figure things out."
The latest loss was Djokovic's first at Key Biscayne since 2013. He missed last year's Miami Open but won the title three consecutive years in 2014-16.