Phelps padded his unprecedented Olympic medal collection Friday, winning his third gold of the London Games and 17th of his career in the men's 100-metre butterfly.
He defeated Chad le Clos of South Africa, who had edged him in the 200 fly earlier in the week.
"I'm just happy that the last one was a win," said Phelps, who increased his career overall medal total to 21. "That's all I really wanted coming into the night."
Phelps now as three gold and two silver medals at these Games, tied in gold medals with teammate Missy Franklin and in total medals with rival Ryan Lochte.
While no one expected him to dominate the way he did at the 2008 Beijing Games, where he won an incredible eight gold medals, it seemed early on that he was ready to pass the torch to Lochte, especially when Lochte soared to gold in the men's 400-metre individual medley while Phelps finished off the podium.
Not so fast, Ryan.
Phelps has won two gold medals over the last two days, further cementing his Olympic legacy and setting up his swan song when he swims the final race of his career, Saturday's 4x100 medley relay.
"My start of the meet wasn't what we wanted, but I seemed to pick up some steam at the end of the meet," Phelps said.
Phelps has led an American team that has dominated in the pool, racking up 14 gold medals and 28 overall.
It was a less glorious day for one of Canada's medal hopefuls, as Dylan Armstrong finished fifth in the men's shot put.
The expectations were high for Armstrong, who just missed a medal in Beijing and reached the top of the world rankings last year. But his best throw was 30 centimetres behind the bronze-medal mark.
"At least it wasn't by a centimetre this time," he said. "If you want to look at it that way. But I'm going to keep my head up and just go hard next year and see what happens there, and hopefully try to get a gold at the world championships.
"You've got to move ahead, this is a tough sport."