Rafael Nadal and Nicolas Almagro advanced to the Brasil Open quarter-finals on Thursday as four seeds were beaten.
Nadal, playing at his second tournament since returning from a long-term knee injury, eased into the last eight with a 6-3 6-4 win over Brazilian qualifier Joao Souza.
The Spanish top seed, runner-up at the VTR Open on Sunday, served five aces and broke once in each set on his way to victory in one hour and 18 minutes.
Nadal is competing at the event for the second time after lifting the trophy in 2005 and meets Argentine Carlos Berlocq in the quarter-finals.
Berlocq overcame Spanish eighth seed Albert Ramos 7-6 (9-7) 6-4 on the clay courts in Sao Paulo.
Three-time champion Almagro, who has won the ATP 250 tournament the past two times, was pushed before edging past Chilean Paul Capdeville 6-4 6-7 (3-7) 6-2.
The Spanish second seed served 18 aces on his way into the quarter-finals, where he will face Argentina's David Nalbandian.
Nalbandian was too good for countryman Guido Pella in a 6-4 6-2 victory.
Argentine Juan Monaco, Brazilian Thomaz Bellucci and Spaniard Pablo Andujar were the other seeds to lose on Thursday.
Third seed Monaco was sent packing by Italian Simone Bolelli, who ran out a 7-5 6-2 winner to set up a meeting with Albert Montanes.
Montanes beat seventh-seeded compatriot Andujar 7-5 6-2, while fifth seed Bellucci was eliminated by Italy's Filippo Volandri, a 6-3 6-2 victor.
Meanwhile, top seed Milos Raonic cruised into the SAP Open quarter-finals on Thursday, while Lleyton Hewitt's exit completed a bad day for the Australians.
Canadian Raonic, the two-time defending champion, served 13 aces on his way to a 6-2 7-5 win over American Michael Russell in the second round.
The 22-year-old secured his maiden ATP World Tour title in San Jose in 2011 and is yet to drop a set in nine matches, including a walkover in the semi-finals two years ago, at the ATP 250 tournament.
Awaiting Raonic in the last eight is Uzbek Denis Istomin after the sixth seed fought his way past German Benjamin Becker with a 6-3 6-7 (5-7) 6-2 win.
The meeting between Raonic and Istomin is a repeat of last year's final, which the big-serving Canadian won in straight sets on the indoor hard courts.
Querrey also advanced to the quarter-finals, but the American needed two hours and 15 minutes to edge Hewitt 7-6 (8-6) 1-6 7-6 (7-4).
The third seed sent down 20 aces but it was two double faults from Hewitt that helped him clinch the third-set tie-breaker.
On a bad day for the Australians, seventh seed Marinko Matosevic and Matthew Ebden were also eliminated.
Matosevic was downed by Colombian Alejandro Falla 6-4 6-4, while Ebden was sent packing after a 5-7 7-5 7-6 (7-1) loss to Belgian Xavier Malisse.
American wildcard Steve Johnson reached his first ATP World Tour quarter-final with a 6-3 6-3 victory over compatriot Tim Smyczek.