Carlos Alcaraz, the world number two, had a successful return to the Rio Open, beating Mateus Alves in a match that was delayed due to a heavy downpour.
Reigning champion Alcaraz had already taken the lead, 6-4, 5-3, on Tuesday when the rain interrupted the match.
On resumption, the 22-year-old Brazilian looked determined to mount a comeback, taking the first game, but Alcaraz held on to his serve and won the match, 6-4, 6-4.
Alcaraz, who made his debut this year and won his seventh ATP title at the Argentina Open last week, said, "It was a complicated match, as the final result shows."
The young Spaniard had lost the first two games but remained upbeat, saying, "Alves is a great player, which he showed here despite the conditions, having to stop and come back the next day.
"It's not easy to play like that. But I'm happy with the win."
In the round of 16, Alcaraz will face Fabio Fognini of Italy, who beat Tomas Barrios of Chile 6-2, 6-3 in another rain-delayed match. Alcaraz acknowledged that Fognini, a talented player with explosive moves, would be a challenge.
"He's very dangerous, with huge talent, very explosive.
"I'll have to stay very focused," said Alcaraz.
The Rio Open is a clay-court tournament, and Alcaraz's victory bodes well for his title defense as he continues to build momentum in the run-up to the French Open in May.