The top-seeded Gonzalez improved to 3-0 against fifth-seeded Monaco. Gonzalez will meet unseeded Pablo Cuevas of Uruguay to try and reach his hometown final for the fifth time.
Gonzalez broke Argentina's Monaco five times without offering a break chance in return in their 56-minute match. The two were supposed to play in last year's final, but Monaco withdrew beforehand after spraining his ankle in the doubles final.
The Chilean star upped his record in the Movistar to 26-5 with titles in 2002, '04 and '08, and a runner-up finish in '03.
Robredo overcame Argentine wild card Juan Ignacio Chela 0-6, 6-3, 6-4, making the decisive break at 3-3 in the last set to reach his first semifinals since he won his seventh ATP title last July at Bastad, Sweden.
Acasuso, the 2006 champion, won 6-4, 6-2 against countryman Sebastian Decoud, a lucky loser who reached his first tour quarterfinals. Acasuso was playing in his first event of the year after missing last month with a right shoulder injury.
Cuevas made it to the last four for the second straight year by beating local wild card Paul Capdeville 7-5, 7-5.
"I'm really happy to reach the semifinals after playing two very difficult matches to qualify and two more difficult matches in the tournament," Cuevas said.