The top-seeded Nalbandian blew a 5-2 lead in the first set. But he powered up his backhand and rolled into a seventh career matchup with Ferrero on Friday.
"I didn't serve very well," Nalbandian said. "I have to try and be more consistent with my game," especially against a worthy opponent like Ferrero, he added.
"We've known each other for a long time. He's the former world No. 1, a great player and it won't be easy to beat him," Nalbandian said.
Former French Open champion Ferrero beat seventh-seeded Marcel Granollers 6-7 (7), 6-0, 6-3 to reach his second quarterfinals in two weeks.
The unseeded Spaniard also made the top four last week in Brazil.
He won the last of his 11 titles in 2003 and has lost nine finals since then. But he's 3-3 against Nalbandian, who won his 10th title last month in Sydney.
Play was halted in the second set for 15 minutes when a stadium light went out, triggering hoots and hollers from the crowd at Buenos Aires Lawn Tennis Club.
After the technical problem was resolved, Chela rallied to take the set 6-3. Robredo then needed to break him three times to win the last set.
Robredo beat Chela en route to the Chile semifinals and then won in Brazil last weekend for his eighth career title. The Spaniard added the doubles title, too.
Also, Franco Ferreiro, the only Brazilian in the tournament, beat fellow qualifier Pablo Cuevas of Uruguay 6-2, 6-4 to post his second win on the main ATP Tour.