"There are no easy matches out there. It was tough, but I'm into the quarters and feeling positive.
"Tomorrow will be even more difficult for sure."
Nadal will next face Serb fifth seed Janko Tipsarevic, who put out Frederico Gil of Portugal 6-2 6-2.
Tipsarevic, who has lost his two previous meetings with Nadal, knows he will be up against the world's best on clay, but goes into the contest with a positive attitude.
"Nadal is absolutely the worst opponent anyone can have on clay," he admitted.
"He's hardly lost a match here. But you have to go for the victory, aiming to just win a few games or a set is not enough.
"I'm playing well, I'm not too tired. I have fuel left in my tank for this match."
Second seed Andy Murray crushed Colombia's Santiago Giraldo in a powerful 6-1 6-2 display to set up a showdown with Milos Raonic.
Murray, a quarter-finalist a week ago in Monte Carlo, reached the last eight again as he builds for the French Open next month.
Murray and No.25 Raonic, who put out two-time semi-finalist Nicolas Almagro 6-3 6-3, had been due to meet in Miami in March but the Canadian suffered an injury and handed the Scotsman a walkover third-round win.
Murray has produced his best career showing in Barcelona this week after previously winning only one match at the Real Club de Tenis.
His win was his 25th of the season against five defeats.
Raonic, the 11th seed who has played fewer than 20 career ATP clay matches, produced an equally one-way third-round win against Spanish sixth seed Almagro in just 67 minutes.
Third seed David Ferrer, three times a losing finalist to Nadal, advanced over Spanish compatriot Albert Montanes 6-0 6-2.
Spanish seventh seed Feliciano Lopez beat Finn Jarkko Nieminen 6-3 6-1 while Japan's Kei Nishikori defeating Spain's Albert Ramos 7-6 (7-2) 6-3.
-AAP
