Top-seeded and defending champion David Ferrer and 2011 champion Nicolas Almagro each posted second-round victories Thursday at the clay-court Copa Claro tennis event.
Ferrer rallied past Argentine David Nalbandian 2-6, 6-4, 6-0.
The 2002 Wimbledon runner-up Nalbandian was last week's Sao Paulo runner-up to the great Rafael Nadal and captured the Buenos Aires championship in 2008.
Meanwhile, the second-seeded world No. 11 Almagro, the runner-up to Ferrer in last year's event, handled Russian Andrey Kuznetsov 7-6 (7-5), 6-2.
Almagro will face Argentine Federico Delbonis in Friday's quarterfinals at Buenos Aires Lawn Tennis Club.
Ferrer beat Almagro in last year's all-Spanish final in this Argentine capital and was the runner-up here in 2010.
In other action involving seeds, No. 3 Stanislas Wawrinka of Switzerland handled Spaniard Daniel Gimeno-Traver 6-1, 6-4, No. 6 Italian Fabio Fognini topped Argentine lucky-loser Marco Trungelliti 7-5, 6-2 and No. 8 Spaniard Albert Ramos got past Argentine Leonardo Mayer 6-3, 7-6 (7-3).
Former Buenos Aires champ and onetime world No. 5 Tommy Robredo also advanced to the quarters after besting Argentine wild card Diego Sebastian Schwartzman 6-3, 6-1 on Day 4.
Also on Thursday, German qualifier Julian Reister edged out Slovenian Aljaz Bedene 6-1, 1-6, 6-2 and the wild card Delbonis straight-setted Spaniard Albert Montanes 6-1, 6-4.
This week's champ will pocket $84,550.