Spanish top seed Carlos Alcaraz abandoned his Rio Open first round match against local favorite Thiago Monteiro on Tuesday due to a right ankle injury.

The two-time grand slam winner rolled his ankle in the opening game of the clash on the Jockey Club Brasileiro's center court.

He initially played on and broke Monteiro's serve, but the Brazilian broke back in the next game.

Alcaraz was in clear discomfort and told the chair umpire he was unable to continue before shaking Monteiro's hand with the score at 1-1.

"I don't know even what to say," Monteiro said. "We didn't want it to be this way."

Alcaraz, who is No. 2 in the world rankings, won the Rio Open in 2022 and finished runner-up at the clay court event last year.

Earlier, former world No. 3 Stan Wawrinka fell to Argentina's Facundo Diaz Acosta 7-5, 6-4.

Others to progress in the ATP 500 tournament on Tuesday included Brazilian Felipe Alves, Dusan Lajovic of Serbia, and Argentine Sebastian Baez.