Phelps notched the fourth-fastest time in the semi-finals of the 200m butterfly, taking the next step in the defence of the title he has won at the last two Games.
On Tuesday he'll be angling to become the first man to win the same Olympic swimming event at three successive Games.
His first attempt at that achievement, in the 400m medley on Saturday, ended with a disappointing fourth-place finish -- his first finish out of the medals in an Olympic final since 2000.
That was the year he finished fifth in the 200m fly as a 15-year-old Olympic newcomer.
"I made my first Olympic team in this," Phelps noted of the 200m fly, an event he has said he holds especially dear.
Phelps owns the four fastest times in history, and his world record of 1min 51.51sec is more than one second faster than the second-best performer in history, Hungarian Laszlo Cseh at 1:52.70.
Even when his goggles filled with water, leaving him virtually blind in the final in Beijing, Phelps held on to win one of his historic eight gold medals.
In addition to its familiarity, Phelps said the race is just a better fit for him now than the punishing 400m medley.
"The shorter races are a lot better for me now that I'm older," the 27-year-old swimming star said.
Phelps, who just scraped into the medley final, said he was satisfied with his fourth-place slot in the fly in 1min 54.53sec.
Japan's Takeshi Matsuda led the way into the final in 1:54.25, followed by South African Chad le Clos and China's Chen Yin.
"You've just got to make sure you make the final and that's all that matters," Phelps said. "I wanted to swim a reserved race and I'm comfortable with that."
Phelps, insisted there was no lingering ill-effect from his 400m medley failure.
He returned to the pool on Sunday to help the United States win silver behind France in the 4x100m freestyle relay.
"I feel a lot better now," Phelps said. "I'm a lot happier. I'm back on track."
The 200m fly treble isn't the only milestone on Phelps' radar. He's also slated to swim the 4x100m freestyle relay on Tuesday, and needs just two medals of any color to take his career total to 19 and surpass the record of 18 medals won by Soviet gymnast Larisa Latynina.
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