Top seed Tommy Haas suffered a surprise opening-round defeat to unheralded Russian Teimuraz Gabashvili at the Delray Beach International Tennis Championships.
The German veteran suffered his third consecutive first-round exit in Florida as he succumbed 7-6 (7/3) 7-5 to the world number 104.
Last year’s runner-up Evgeny Korolev recovered from a mid-match slump to overcome Nicolas Lapentti 6-2 1-6 6-1.
Korolev, the fifth seed, won just six points on serve in the second set but fought back strongly to ensure his progress with an impressive third set.
Floridian Wayne Odesnik secured a 6-3 6-2 win over Rajeev Ram despite twisting his ankle early in their match.
Odesnik suffered the injury at 3-1 ahead in the opening set although it did not prevent him moving through.