Giraldo looked set to provide a tough challenge for the top-ranked Nadal when he broke the Spaniard's serve to tie it 3-3 in the first set. But the five-time champion responded by breaking right back and dominated the rest of the match on the clay court, his surface.
"Giraldo is an unpredictable player," Nadal said. "He has very quick hands, hits flat and has a powerful drive. If he develops he can be one of the best."
Nadal improved his record in Barcelona to 28-1 and will play the seventh-seeded Monfils, who beat fellow Frenchman Richard Gasquet 6-4, 7-6 (7).
"You have to remember that [Monfils] is a player who has made it to the semifinals of Roland Garros, he's in the top 10," said Nadal. "I imagine that tomorrow he will come out aggressive, so I will have to make him play as far back as possible."
Monfils has one victory in seven tries against the world's top-ranked player.
Even so, the 24-year-old Monfils said he will treat it like any other match.
"It doesn't matter if it's Nadal or any other player, I face the match like any other," said Monfils, who is playing only his second tournament since recovering from a wrist injury. "I feel good and that I am close to returning to my best level.
"So far this season I have played four matches on clay and this has been my best," he said.
Ferrer battled gusting winds to break Hanescu in the eighth game of the first set and then cruised to victory.
"It wasn't a good day because it was very windy, but I was steady with my serve, so it was a good day," said the two-time finalist.
"I knew that this match could have a prize and I tried not to think about it, but I'm not made of stone," the 25-year-old Spaniard said. "This was my third shot at breaking into the top 10, and it was great to finally do so at home in front of my people."
Almagro will face Juan Carlos Ferrero after the former No. 1 downed Simone Vagnozzi of Italy 7-6 (3), 4-6, 6-4 in his third match since returning from wrist and knee surgery in October.