Top-seeded David Ferrer of Spain outlasted hometown favourite David Nalbandian in three sets to reach the quarterfinals of the Copa Claro in the Argentine capital.
Ferrer, the defending champion and No. 4 in the ATP rankings, won 2-6, 6-4, 6-0 and will face Fabio Fognini of Italy in the quarterfinals on Friday.
No 2 Nicolas Almagro of Spain also reached the quarterfinals, defeating Andrey Kuznetsov of Russia 7-6 (5), 6-2. Almagro faces Federico Delbonis of Argentina in the next round.
Ferrer and Almagro met in last year's final, and they are headed that way again.
Nalbandian started quickly winning the first set but began to struggle to hold serve in the second. Ferrer took that set, breaking Nalbandian in the final game. After that, the Argentine offered little resistance going down 6-0.
"David (Nalbandian) is a player who dominates from the start," Ferrer said. "I knew to beat him it would have to be a long match - beating him physically."
Almagro also struggled in his first set.
"It was not a very good match for me," he said. "The important thing is being in the quarterfinals again."
Almagro won this tournament two years ago and was the runner-up last year to Ferrer. This is his sixth appearance in the quarterfinals.
"It's always nice coming here," he said. "I feel really good and I feel loved by the people here. Six times in the quarterfinals says a lot, and a title, too."