Top seed James Blake eased into the US Clay Court Championships second round but fellow American Sam Querrey, the fourth seed, made an early exit on Wednesday.
Blake, the world number nine, beat Japanese wildcard Kei Nishikori 6-4, 6-4 in an evening match to set up a meeting with 15-year-old American Ryan Harrison on Thursday.
Harrison had stunned Uruguay's Pablo Cuevas 6-4, 6-3 in Monday's first round to join Spaniard Rafael Nadal and Frenchman Richard Gasquet as the only players since 1990 to win ATP matches under the age of 16.
Big-serving Querrey squandered a 2-0 lead in the decisive set before losing 5-7, 6-4, 6-4 to Chilean Nicolas Massu in a tight contest lasting two hours, 48 minutes.
Massu, making his third appearance at an event where he reached the final on his debut in 2000, broke back twice in the third set to secure victory.
"I played well and it could have gone either way," Querrey, 20, told reporters. "It was a tough match. I didn't serve my best but, other than that, it was pretty good.
"I'm not too disappointed," added the towering American who clinched his first ATP title at last month's Las Vegas Open.
Massu, 28, next faces Brazil's Marcos Daniel, a 6-3, 6-4 winner over Serb Viktor Troicki.
In other first-round matches, Australia's Peter Luczak beat qualifier Harel Levy of Israel 6-4, 6-4 and Chilean Paul Capdeville brushed aside Argentina's Diego Hartfield 6-0, 6-4.
Eighth-seeded Spaniard Oscar Hernandez scraped past American Donald Young 6-4, 6-4 in a second-round encounter.
Mardy Fish, the third seed, was playing fellow American Hugo Armando in an evening match for a spot in the third round.
