With Roland Garros - a key marker for holder Federer and four-time winner Nadal - starting a week from Sunday, the countdown is taking on extra urgency for the old rivals.
Number one Federer came through against fellow Swiss Stanislas Wawrinka, carving out a 6-3, 6-1 win after gaining early momentum by breaking his Davis Cup teammate on a fourth opportunity in the second game of the match.
From then on, Federer's huge game began to flow as he took aim at repeating his breakthrough title at the Caja Magica from a year ago.
Federer iced the first set after 42 minutes with his fifth ace and moved purposefully into the second with a break in the opening game and another in the third on his way to the comfortable win.
"I'm very happy with how I played, it's never easy playing a countryman," said Federer, who now faces Latvian Ernests Gulbis, who put out Feliciano Lopez 6-2, 7-6 (7/0).
Gulbis defeated Federer at the Rome Masters last month.
"To beat Stan on his best surface is excellent. I'm feeling great about my play now," added Federer.
"I haven't had that many matches in the last few weeks, but I won the French Open and no matter how tough the clay season is, I can walk around with a smile on my face."
Nadal reached the quarter-finals for the sixth consecutive year when he smothered the huge serving of American 13th seed John Isner to claim a 7-5, 6-4 victory.
The Spanish second seed, who was the 2005 champion when the event was played on indoor hardcourt, held Isner to a mere 11 aces on a chilly day with the roof closed in case of rain.
Nadal has already lifted titles at his first two clay tournaments in 2010 - the Masters 1000 events in Monte Carlo and Rome - as he builds up towards the French Open.
"It was a dangerous, difficult match," said Nadal, who next faces French 12th seed Gael Monfils, a winner over Guillermo Garcia-Lopez 7-6 (7/5), 6-4.
Nadal won his last match against Monfils in the US Open fourth round last year despite suffering an abdominal injury.
"Gael is a charismatic player, he plays fast and aggressive. He can change strategy suddenly and is very confident."
British third seed Andy Murray eased past Romania's Victor Hanescu 6-2, 6-1.
"Today was better than my previous match," said the Scot, who went 1-2 at the start of the clay season and now faced Spain's David Ferrer, a 6-3, 6-2 winner over Marin Cilic.
"I served better and made less mistakes. I'll have to do even better tomorrow," he said of Ferrer, who beat him in Rome a fortnight ago.
In the WTA event, Australia's Samantha Stosur and China's Li Na stormed into the last eight.
Eighth seed Stosur stopped Swiss Patty Schnyder 7-6 (7/3), 6-2 while Li, the 13th seed, put out Alona Bondarenko of the Ukraine with a 6-3, 6-4 win.
Stosur next faces a test against fourth seed Venus Williams, against whom she stands 0-3 from 2007 and 2008 meetings.
Li will play Israeli Shahar Peer, who defeated Spain's Arantxa Parra Santonja 7-5, 6-2.
Stosur remains a huge force on the spring clay after winning 14 of her last 15 matches on the surface, taking the title last month at Charleston and playing the final in Stuttgart against Justine Henin.
The 2009 Roland Garros semi-finalist will arrive in Paris as the highest-ranked Australian woman since Wendy Turnbull was classed fifth in February 1984.
Arvane Rezai of France needed seven match points to hold off Andrea Petkovic in a 6-4, 7-6 (10/8) victory while third seed Jelena Jankovic advanced over Anabel Medina Garrigues of Spain 6-2, 6-0.