Home favourite Thomaz Bellucci received a standing ovation after dismissing Rio Open presented by Claro top seed Kei Nishikori 6-4, 6-3 on Tuesday.
Nishikori reached the Argentina Open final last week and won their only previous meeting on the clay at the 2015 Roland Garros in straight sets, but the top-ranked Brazilian put in a commanding display to defeat the World No. 5.
"Actually everything didn’t work well," said Nishikori. "Probably the condition changed a lot from last week: bounce really high and the balls are really heavy. The ball is the most difficult to adjust. I couldn’t feel anything today. I think it wasn’t my day."
Bellucci, quarter-finalist in 2014, earned a second-round encounter with countryman Thiago Monteiro. The World No. 85 defeated Gastao Elias 2-6, 7-6(4), 6-4.
Watch Full Match ReplaysWorld No. 8 Dominic Thiem made his way safely through his opening match, defeating former World No. 8 Janko Tipsarevic 6-4, 7-5. The second seed, a semi-finalist last year on his tournament debut, capitalised on three of his five break points en route to the one hour, 35-minute victory. Thiem next faces another Serbian, Dusan Lajovic, as he looks to reach his fourth quarter-final of 2017.
Alexandr Dolgopolov maintained his title-winning form from Buenos Aires last week with a 6-4, 6-4 victory over 2015 champion David Ferrer. Sixth seed Ferrer led their FedEx ATP Head2Head 9-3, however, Dolgopolov managed to repeat his 2014 win in Rio over the Spaniard to advance into the second round.
Two other Spanish seeds avoided the fate of their countryman. Fourth seed Pablo Carreno Busta ousted Brazilian wild card Joao Souza 6-3, 6-2, while fifth seed Albert Ramos-Vinolas beat Stephane Robert 6-2, 6-0. Carreno Busta goes on to face recent Quito champion Victor Estrella Burgos, a 6-2, 7-5 winner over 2016 Rio finalist Guido Pella. Ramos-Vinolas will take on Fabio Fognini, who defeated veteran Spaniard Tommy Robredo 6-2, 6-4 to avenge a straight-sets loss in Buenos Aires.
Argentine Federico Delbonis improved to a 4-0 FedEx Head2Head record against Italian Paolo Lorenzi as he rallied for a 4-6, 6-1, 6-4 win in two hours and 13 minutes.