(CNN) -- World No. 2 Rafael Nadal remains on course for a semifinal showdown with Andy Murray at the French Open after both progressed into the last eight on Monday.
Nadal, seeking a record seventh title at Roland Garros, set up a clash with fellow Spaniard Nicolas Almagro after posting his fourth successive straight-sets victory of the clay-court event.
Having celebrated his 26th birthday on Sunday, Nadal demolished Argentine 13th seed Juan Monaco 6-2 6-0 6-0 to send a real message of intent to his main rivals.
He won 17 games in a row to take his overall record at the tournament to 49-1.
"In my opinion, he was unlucky in the first set. That's my feeling, 6-2 was too much. Later, for sure I was very happy the way I played. I feel very, very sorry for him," Nadal said.
"I think he's playing probably the best tennis of his career, but probably not today, especially in the last set. I saw him suffering a little bit on court at the end. He's one of my best friends on tour."
Fourth seed Murray had to fight harder against home hope Richard Gasquet, coming from behind to set up an intriguing quarterfinal with in-form Spaniard David Ferrer.
"We've had some great matches, I've known him since I was a young kid, he is an unbelievable talent," said Murray, who leads their meetings 5-4 but has lost all three on clay.
"Every time I play against him I expect a very tough match. I'll have to play really well to win."
Sixth seed Ferrer crushed compatriot Marcel Granollers 6-3 6-2 6-0, while 12th seed Almagro defeated Serbia's world No. 8 Janko Tipsarevic 6-4 6-4 6-4.
"That win is one of the best moments of my career," said Almagro, who has lost twice to Nadal in French Open quarterfinals.
"He's the man on clay, and we are trying to be close to him. We are working hard to do our best. It's another match, and I'm ready to fight."
France will have one competitor in the last eight, as fifth seed Jo-Wilfried Tsonga completed a 6-4 7-6 (8-6) 3-6 3-6 6-4 win over Swiss No. 18 Stanislas Wawrinka after the match was halted due to bad light on Sunday.
Tsonga, seeking to become the first French male to win the tournament since Yannick Noah in 1983, will play world No. 1 Novak Djokovic in his first quarterfinal appearance at Roland Garros.
The Serbian is seeking to become the first man since 1968 to hold all four grand slam titles, but has never made it to the final in Paris.
"It's going to be a very difficult match. But obviously I'll fight like a lion and we'll see the result," Tsonga said.
Argentine ninth seed Juan Martin del Potro also progressed after a delayed match, with the 2009 U.S. Open champion beating Czech No. 7 Tomas Berdych 7-6 (8-6) 1-6 6-3 7-5.
The 23-year-old will next face world No. 3 Roger Federer, who beat him in the 2009 French Open semis before winning the title for the first and only time to complete his collection of grand slam crowns.