Juan Martin del Potro suffered a surprise early exit at the ATP Sony Open, losing to Tobias Kamke in the second round of the Masters event in Miami.
The fifth seed - playing in his opening match in the tournament after being given a first-round bye - tumbled out 7-6 (7/5) 6-1 in a rain-interrupted clash.
Del Potro, who had made it through to the final at Indian Wells last week, looked to be on course when he led by a 5-2 scoreline in the opening set.
However, the world No 7 fell apart from a position of such strength. He wasted two set points before allowing Kamke to take four of the next five games, leading to a keenly-contested tie-break that the underdog won.
The German then dominated in the second set when play resumed following a weather delay, meaning he is through to the third round of a Masters event for the first time in his career.
"The second set, after the break, I felt even better," Kamke told the ATP Tour's official website. "He didn't play obviously his best tennis, but still I think I did a good job and pretty satisfied with that."
Meanwhile, Novak Djokovic shrugged off a delayed start to his match with Lukas Rosol, brushing aside the Czech 6-1 6-0 to reach round three.
The world No 1, beaten by Del Potro in the last four in Indian Wells, his only defeat of the year so far, needed just 53 minutes to wrap up victory in the night match that had been held up by both the weather and a power cut.
"It is a great start," the Serbian said afterwards. "After Indian Wells, I tried to rest. There are different conditions here, but tonight was perfect for tennis. I enjoyed every moment of it and I love this court."
David Ferrer was given a free route through to the third round after his scheduled opponent Dmitry Tursunov withdrew from the contest due to illness.
The Spaniard received a bye in the first round, meaning his first competitive action of the tournament will come in the last 32 against Fabio Fognini.
No 32 seed Fognini recorded a straightforward 6-4 6-1 win over Michael Llodra, while fellow seeds Tommy Haas and Kei Nishikori also advanced to the third round.
Ukrainian Alexandr Dolgopolov defeated Russia's Nikolay Davydenko 6-2 6-3 and seventh seed Janko Tipsarevic saw off Dudi Sela 6-2 6-4.