Querrey outlasted Nicolas Massu 6-3, 3-6, 6-4 and got a break as well when No. 1 seed Fernando Gonzalez was knocked out of the event.
Gonzalez fell to Horacio Zeballos, the sixth seed, 6-4, 6-4. Gonzalez won this tournament 10 years ago.
Defending champion Lleyton Hewitt also lost to Juan Ignacio Chela 6-4, 6-3.
In the semifinals, Querrey will meet Wayne Odesnik, who defeated Xavier Malisse 6-4, 6-1.