In fact, before diving into the pool for the 200-meter butterfly, he didn't even bother to shave the thick goatee he had been growing for several weeks. He hadn't cut his hair or shaved any part of his body, a pre-race maneuver for swimmers to reduce drag.
What happened next defied reason: Phelps broke his world record.
His coach, Bob Bowman, said later he knew, right then, that Phelps might be setting the stage for a dominant performance at the FINA World Championships. But after Phelps grabbed seven gold medals and four world records in Australia, even Bowman was a bit surprised.
So with Phelps returning to the Missouri Grand Prix today, a four-day meet held at the University of Missouri's Mizzou Aquatic Center, is it possible we could see a repeat? A curtain-raiser that hints at what we might see in Beijing at the Olympics just six months from now?
"I don't think we'll see any world records fall," Phelps said. "I just want to have a decent meet, put up some respectable times and see where I'm at."
Still, with Phelps, it's important to keep in mind that anything is possible. The Missouri Grand Prix is the first long-course meet for Phelps and Towson's Katie Hoff since the USA Swimming National Championships in Indianapolis in August.
Phelps will be looking to show that his wrist injury -- a broken bone that occurred in October when he slipped while climbing into a car -- is behind him.
"I don't think it's even an issue anymore," Bowman said. "If you look at how he swam in Long Beach [in January], he was faster there this year than he was a year ago."
Phelps and Hoff also will debut new swimsuits that were designed in cooperation with NASA. The Speedo Fastskin LZR Racer, which Hoff and Phelps showed off in New York this week at a news conference and on an appearance on NBC's Today show, claims to reduce drag in the water by as much as 10 percent and increase oxygen intake. It's not likely to shave huge chunks of time off Phelps' and Hoff's best events, but at the highest level, even a few tenths of a second can make a difference.
"It feels like a rocket when you come off the wall," Phelps said. "It's like wearing a space suit. I'm excited to see the results."
Hoff said: "I love it. I love it so much better [than last year's suit.] ... The first time I dove in the water, I popped up with a smile on my face. I feel like I'm right on top of the water and the water is going past me and not slowing me down at all."
The event, which will feature practically every elite U.S. swimmer, will also be an interesting preview of what it will be like to swim this year's Olympic schedule. In Missouri, as in Beijing, finals will be held in the morning.
Bowman said the key to racing in the morning is getting your core body temperature where you want it quickly, something Phelps has been working on.
"He's not a morning person, which is a lot like most kids his age," Bowman said. "But with a hot shower and some adrenaline, I think those things can help make the adjustment."
Sun reporter Candus Thomson contributed to this article.