World number one Rafael Nadal and number three Roger Federer cruised into the last-16 stage of the Sony Ericsson Open in Key Biscayne, Miami.

Nadal won a routine straight-set victory against fellow Spaniard Feliciano Lopez 6-3 6-3 after Federer, in a hard-fought encounter, had beaten Argentine Juan Monaco 7-6 (7-4) 6-4.

If things pan out, there could a potential Nadal - Federer thriller in the semis.

Elsewhere, seventh seed Tomas Berdych also progressed with a thrilling 7-6 (10-8) 7-5 win over Carlos Berlocq after world number two Novak Djokovic and Argentine Juan Martin del Potro won both advanced on Sunday.

Belgian Olivier Rochus saw off 13th seed Mikhail Youzhny 1-6 6-3 6-3 and will face Federer next while Nadal will face the winner of the potentially explosive match between Alexandr Dolgopolov and Jo-Wilfried Tsonga.

After the win over Lopez, Nadal said he was more focused on landing his first title since October last year than defending his number one status in the world rankings.

I know I'm number one in the ranking right now, but I am number six this year. I didn't play for a month, he said. For me, every year I start from zero. Right now I am number six, and I would love to play well in the next tournaments and have the chances to be in a better position.

After his victory, Federer, who recently lost his number two spot in world rankings to the in-form Djokovic, claimed he was happy with his performances and also admitted he wasn't faced by the potential semi-final clash with Nadal considering he is in unfamiliar territories as third seed.

He said, I've been in the semis with Rafael beforehand, so it's not something that's completely new to us. People talk about it like it's not been a good last six, seven months (for me) just because I'm number three in the world.

But Rafa and Novak have been exceptional of late, and I've done really, really well. So it's up to me to step it up or just maintain that level of play and I'll get my chance.