Top seed Williams shrugged off a funny turn midway through her third-round match against Russian teenager Anastasia Pavlyuchenkova before recovering her senses to win 6-1, 1-6, 6-2 and join sister Venus in the last 16.
Fellow American Roddick was trounced 6-4, 6-4, 6-2 by Teimuraz Gabashvili -- his misfiring game no match for the flashy Russian or the cool, breezy conditions that returned to Roland Garros after the glorious sunshine of Frantic Friday.
Roddick angrily threw his spare racquets to his entourage after dropping his serve in the seventh game, complaining about string tensions. By the time they returned to a chilly Court Suzamme Lenglen, it was virtually all over.
Spain's David Ferrer also joined Roddick on the casualty list, the ninth seed surprisingly beaten in straight sets by Austrian Jurgen Melzer, who now faces Gabashvili for a place in the quarterfinals.
Rafael Nadal broke down some typically stiff resistance from Australian Lleyton Hewitt to record a 6-3, 6-4, 6-3 victory in their third-round clash on a chilly Saturday afternoon.
After Friday's champagne tennis when organisers got the tournament schedule back on track with a feast of top seeds in action, the middle weekend began with a hangover.
Hopes that home favourite Aravane Rezai would lift the mood evaporated when she lost what amounted to a sudden death shoot-out against Russia's Nadia Petrova.
Starting at 7-7 in the deciding third set after darkness interrupted a thrilling match the previous evening, 15th seed Rezai was back off court in 15 minutes after Petrova held her nerve to prevail 10-8.
Marion Bartoli also lost her third-round match against Israel's Shahar Peer to leave Jo-Wilfried Tsonga as the only home player left in the singles draw.
Peer will face Serena for a quarterfinal berth but at one stage, Pavlyuchenkova looked the more likely winner of the day's opening match on Phillipe Chatrier court.
Williams lost her opening service game of the morning to the 18-year-old but rattled off the next six in what looked to be shaping up as gentle Saturday morning work-out.
The 28-year-old, shooting for a 13th Grand Slam singles title, then slumped 5-0 down in the second set and called for the trainer and the doctor at the changeover.
After having her pulse taken and her temperature checked, she emerged rather gingerly before losing the set.
She resisted some aggressive play early in the third and saved two break points before regaining control, clinching victory in one hour 48 minutes.
By reaching the fourth round, Serena is guaranteed holding the world number one ranking from sister Venus, whatever happens in the rest of the tournament.
Bad day for Bhupathi
Leander Paes and Rohan Bopanna scored contrasting wins with their respective partners but Mahesh Bhupathi exited along with Max Mirnyi from the men’s doubles on Saturday.
Defending champions and third seeds Paes and Lukas Dlouhy of Czech Republic booked a pre-quarterfinal berth with a 6-4, 3-6, 6-3 win over unseeded pair of Swiss Yves Allegro and Andreas Beck of Germany. However, Bhupathi and Mirnyi had disappointment in store as they lost 4-6, 6-7 (4) to Spanish pair of Marc Lopez and Pere Riba.
Bhupathi’s day ended in more misery after he crashed out from the mixed doubles first round event. Bhupathi and his American partner Lizel Huber came up with a listless performance against unseeded rivals Yung-Jan Chan and Eric Butorac, losing 1-6, 4-6 in 55 minutes.
However, Paes advanced to the second round with his partner Cara Black after an easy 6-3, 6-3 win over the local pair of Pauline Parmentier and Marc Gicquel.
Earlier, Bopanna and his Pakistani partner Aisam-ul-Haq Qureshi scored an easy 6-2, 6-3 win over Italian Fabio Fognini and American Michael Russell, and they will next meet 15th seed and local favourite Julien Benneteau and Michael Llodra.