Six-time champion Novak Djokovic ran out of gas in a straight sets loss to Benoit Paire, while the red-hot Juan Martin Del Potro won his opening match at the ATP Miami Masters on Friday.
It was another setback for the Serbian star Djokovic as he bids to return from the elbow injury that sidelined him for six months and finally saw him have "minor" surgical intervention after a disappointing Australian Open.
"I'm trying, but it's not working," said Djokovic, who lost his opener 6-3, 6-4. "That's all it is. I mean, 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 to play. Just, it's impossible at the moment. That's all."
While Djokovic is struggling, world number six Del Potro is headed in the opposite direction. The 29-year-old Argentine showed why he is the hottest player on the ATP Tour right now with a 4-6, 7-5, 6-2 win over Robin Haase in his second round match.
Paire broke Djokovic at love to seal the win, Djokovic dumping a backhand into the net on the Frenchman's first match point.
"I felt I started the match well, first six games," Djokovic said. "Then I just ran out of gas. He was serving well. I just wasn't able to break him down. He was just coming up with the good shots at the right time. It happened very fast."
Djokovic had also lost his opening match at the Indian Wells Masters last week. But he was encouraged in Miami this week to find himself playing without pain for the first time "in years."
He said a lack of match fitness was "one of the things" preventing him from gaining any steam in his bid to return to his top form.
But he said that in attempting to play through injury for so long, "I compromised my game and the movement and everything ... I'm trying to figure things out.
"I wanted to come to Indian Wells and Miami because I wanted to see whether I can play a match," he said. "I love playing on the hard court. I wanted to get a couple of tournaments before the clay court season starts.
"I obviously wasn't ready for that."
Although he had planned for the two Stateside hardcourt tournaments to be a precursor to a full clay court season, Djokovic sounded unsure after the defeat.
"That was the plan," he said when asked if he felt ready to head into the Monte Carlo Masters Aril 14-22. "But let's see what happens."
Former US Open winner Del Potro extended his win streak to 12 straight matches as he seeks his third straight ATP title after winning back-to-back in Acapulco and Indian Wells.
Del Potro blasted five aces and won 79 percent of his first-serve points in the two hour and nine minute match.
Del Potro moves on to the third round where he will battle 26th seeded Kei Nishikori who needed three sets to eliminate Aussie qualifier John Millman 7-6 (7/4), 4-6, 6-3
In other matches on Friday, second seed Marin Cilic, of Croatia, eased past Pierre-Hugues Herbert, of France, 7-5, 6-3; Canada's Milos Raonic rolled over Swede Mikael Ymer 6-3, 6-3; third seeded Grigor Dimitrov defeated Maximilian Marterer 4-6, 6-2, 6-1; and South Korea's Chung Hyeon toppled unseeded Matthew Ebden 6-3, 7-5.