Hall and Ervin hit the wall at the same time -- 21.98 seconds -- for the first tie in Olympic history in either of the sprint events.

"That makes us the best in the world in no uncertain terms," Ervin said.

Indeed, the Americans reinforced their reputation as the world's swimming superpower with one day remaining in the pool.

Pieter van den Hoogenband of the Netherlands took bronze in 22.03.

Alexander Popov of Russia was sixth in 22.24, failing to win an unprecedented third consecutive Olympic title.

Hall, of Phoenix, and Ervin, of Valencia, Calif., are training partners in Arizona. Ervin was quickest off the blocks in the final. Hall was right behind him.

"I don't mind sharing the gold medal podium," Hall said. "It couldn't have happened to a nicer guy, a guy I practice with all the time. It was like another day of practice."

Ervin, who at 19 was the youngest swimmer in the eight-man final, is the first swimmer of black heritage to make a U.S. Olympic team.

"I've always been proud of my heritage. I don't think about it very much," he said. "To me, it's not that big a deal."

Hall, the silver medalist to Popov four years ago in Atlanta, was actually faster at the U.S. trials in August, where his time of 21.76 set an American record and was the second-fastest in history.

Ervin also finished second to Hall at the trials with the third-quickest time in history.

"The 50 was my place to shine," Ervin said. "Thankfully, I did."

By tying for the gold, Hall avenged his third-place finish behind Van den Hoogenband and Popov in the 100 freestyle Wednesday.

Hall's medal capped a troubled four years since Atlanta. He was suspended for marijuana use by the sport's international governing body, then diagnosed with diabetes. He requires several insulin shots daily to keep his blood sugar levels in check.

"There's a million reasons why I shouldn't be here, like diabetes," said Hall, whose father, Gary, was a three-time Olympic swimmer. "To come out on top is such a thrill."