The unseasonal rain that washed out most of Monday's matches gave way to brilliant sunshine but the two world number ones were caught in their own storms.
Federer survived a real scare from Russia's Igor Andreev before winning his opening match 4-6, 6-2, 7-6, 6-0 while Williams lashed out at officials after her 6-2, 6-1 win over Poland's Urszula Radwanska.
Sweden's French Open finalist Robin Soderling was the biggest name to fall on a day when eight seeds were buried and a little-known Irishman suddenly found himself in the spotlight.
The notion that Federer's air of invincibility is diminishing has been one of the popular topics of conversations in the build-up to the first grand slam of 2010.
The Swiss master has repeatedly dismissed the notion his motivation might be waning after he achieved his lifelong goals last year -- including a first French Open crown and a record 15th grand slam title at Wimbledon -- but his performance against Andreev would have done little to silence the doubters.
Russia's Nikolay Davydenko, who has beaten both Federer and Rafael Nadal twice in the same tournament in recent months, said he believed he was now the player everybody feared.
"I have more confidence," the sixth seed said after a 6-1, 6-0, 6-3 win over Germany's Dieter Kindlmann. "I know everybody is scared to play against me."
By his own standards, Federer was below his best and got a lucky break when Andreev failed to serve out the third set but he almost laughed when he was asked if he feared Davydenko.
Serena hardly broke sweat as she opened her title defence with a comfortable win on the Rod Laver Arena, extending her perfect record of never losing in the first round of a slam, but saved her best shots for the post-match news conference.
Still bristling after being handed a record fine for her expletive-laden outburst at a lineswoman in New York, the American was adamant that she had been unfairly treated. "I don't know whoever got fined like that. People said worse, done worse. I think it was a bit much," she said.
She was joined in the second round by her elder sister Venus, one of many recent Australian Open finalists who won on Tuesday, including Lleyton Hewitt, Ana Ivanovic and Marcos Baghdatis.
Novak Djokovic, the 2008 champion, also made an impressive start when he beat Daniel Gimeno-Traver 7-5, 6-3, 6-2 in a clear intention for his plans over the next fortnight.
Eighth seed Soderling, struggling with an elbow injury, joined first day loser Maria Sharapova in making an early exit when he lost 5-7, 2-6, 6-4, 6-4, 6-2 to Spain's Marcel Granollers. Fabrice Santoro bid farewell to the game after his final appearance. "I was very happy to come back one more time here. No regrets," he said after his 7-5, 7-5, 6-3 loss to Marin Cilic.
His 6-4, 3-6, 6-2, 6-1 win over Taiwan's Lu Yen-hsun thrust him into an unfamiliar world.
Sania ousted
Sania Mirza crashed out after suffering a straight-set defeat in the first round at the hands 26th seed Aravane Rezai of France. The unseeded Indian lost her opening round 4-6, 2-6 in one hour and nine minutes to world number 27 opponent.
The first set could have gone either way with both the players getting an equal number of opportunities to break. However, Sania missed all the four breakpoints while the French woman rode on one break to shoot into lead.
In the second set too, Sania got four chances to break her rival but could convert just one while she dropped her serve thrice.
