Agassi clattered former Melbourne Park runner-up Thomas Enqvist 6-0, 6-3, 6-3 in a breathtaking display while world number one Roddick unleashed his firepower on Taylor Dent to win 6-2, 6-0, 6-2 in just 71 minutes.
"I think I played pretty good tonight," Roddick said in a classic case of understatement.
The pair were joined in the fourth round by women's top seed Justine Henin-Hardenne and tortured Tartar Marat Safin, who fought his personal demons for more than three-and-a-half hours before beating Todd Martin 7-5, 1-6, 4-6, 6-0, 7-5 in a dramatic encounter.
Henin-Hardenne needed all her confidence to beat free-hitting Russian Svetlana Kuznetsova 6-2, 7-5. The world number one had trailed 5-3 in the second set before getting back on track.
"It was a good fight," the Belgian said. "She had nothing to lose and put me under a lot of pressure... she's a tough opponent.
Henin-Hardenne plays Italian qualifier Mara Santangelo next.
Sweden's Enqvist had won five of the his previous nine matches with Agassi but on Friday it was one-way traffic.
"I had a real sense of urgency," Agassi said.
"You go out there with a real clear idea of what you want to do when you've played each other so many times.
"But every day is a new day. I played well today and I executed everything I wanted to. Everything felt real good from my point of view."
The win stretched the American's unbeaten run in Melbourne to 24 matches. He first won the title in 1995 and added three more in 2000-01 and 2003. Injury prevented him from playing Down Under in 2002.
U.S. Open champion Roddick, looming as the man to beat here, fired only four aces and 30 clean winners past Dent but put his fellow-American under so much pressure that he committed 26 unforced errors and 11 double faults.
"That was the worst ever. This is going to sting for a little bit," said Dent.
"Andy just exploded and didn't let me get back into it."
"BIG RED"
Former world number one Safin, now ranked a lowly 86th after an injury-plagued 2003, could not claim to have played his best
Known as "Big Red" for his booming serve and imposing presence, Safin was at times brilliant but also often resembled a park player, frequently venting his anger by slamming his racket into the ground.
"You know... (it) was frustrating," he said. "I couldn't find a way to break him, I was looking for so many ways I got a bit upset."
A former U.S. Open champion and finalist here in 2002, the Russian will tackle another American in round four, James Blake.
Blake is sporting a shaved head and his dreadlocks are being auctioned for charity.
He has suffered no apparent Samson effect by cutting his locks and stayed strong on Friday to whip Frenchman Olivier Patience 6-1, 6-3, 6-2.
France had more luck in the women's draw where, despite a problem with her left leg, Amelie Mauresmo beat Spain's Anabel Medina Garrigues 6-1, 6-2.
HEAVILY MASSAGED
Runner-up in 1999, the fourth seed was always in control of the match but needed a medical time-out midway through the second set after suffering problems with her lower left leg.
She resumed playing after the leg had been heavily massaged and quickly reeled off the last three games to wrap up victory in 61 minutes.
Mauresmo plays Australia's Alicia Molik next. Molik beat Luxembourg's Claudine Schaul 6-7, 6-1, 6-2.
Lindsay Davenport also advanced, breezing past fellow American Laura Granville 6-4, 6-0.
The fifth seed, winner in Melbourne four years ago and the only former champion in the women's draw, struggled with her serve but still had too much power for her 54th-ranked opponent.
The 27-year-old Californian will play 11th seed Vera Zvonareva of Russia in the fourth round.
Gustavo Kuerten's joy at achieving his best Australian Open performance was short-lived when the former world number one was beaten by Paradorn Srichaphan.
The Thai 13th seed cantered through 6-3, 7-5, 6-4 against the three-times French Open winner.
Until this year Kuerten had not progressed beyond the second round in seven previous visits and it appears Melbourne Park is not destined to be a happy hunting ground for the Brazilian.
Paradorn will next run into Agassi.
