BEIJING — For Usain Bolt and Asafa Powell, it will still be a dream matchup. For Tyson Gay, a bitter disappointment.

The American record-holder and defending world champion failed to make the finals of the Olympic 100-meter dash today, finishing .02 second out of fourth place in his semifinal heat and making an early exit from one of the most highly anticipated events of the Beijing Olympics.

Starting in the outside lane, Gay got a good jump from the blocks and was in the mix early in the race, but he never showed any burst, was overtaken by Powell and Richard Thompson and outleaned to the line by American Darvis Patton, who finished in 10.03 seconds.

“I did my best,” Gay said. “I don’t have any excuses.”

It means Gay’s only chance at Olympic medals will come in the relays. He didn’t qualify for the 200, in which he was also the 2007 world champ, because he pulled up lame in prelims with a strained left hamstring at the Olympic trials six weeks ago.

Gay, who set the American 100 record at 9.77 earlier at the trials, also ran a wind-aided 9.68 — the fastest time in any conditions — in the trials’ 100 final.

In Beijing, he insisted the hamstring was fine and he was ready to go, and he did make it through the first two rounds Friday without a problem.

But on Day 2, in front of a packed house at the Bird’s Nest, he did not run like a champion. The photo at the finish showed a sliver of daylight between him and Patton.

“I’m pretty upset,” Gay said. “When I get back to the village, it’s really probably going to set in. My family is here. Everyone at home is supporting me, and I just feel I let them down a little bit.”

The Jamaicans had no such trouble.

Powell won that second semifinal in 9.91.

Bolt eased through, as well. His sprint in the first semifinal was a breeze. He finished in 9.85 seconds, .10 better than American Walter Dix, and that despite slowing down as he approached the finish, looking to his left, his right and then his left again to see if anybody was near.

Nobody was.

“He’s on fire,” Gay said of Bolt. “He just has that rhythm. He’s in the zone. When you get that way, you kind of feel unstoppable.”

Saturday night’s scene wasn’t all too different from May 31 in New York, when Bolt ran 9.72 seconds for the world record, routing none other than Gay.

Gay said he refocused himself after that embarrassment, and his early showing at Olympic trials proved that.

He put up the two gaudy times and set himself up as a serious threat to Bolt and Powell, who held the world record himself for three years. Then the hamstring sent Gay sprawling, and his lead-in to the Olympics was disrupted.

He went to Germany for therapy and said he would run in a July 25 race in London but pulled out, saying he’d rather run at 100% at the Olympics than at 85% “just to see how I’m doing.”

So, everybody got to find out together on the world’s biggest stage and the result wasn’t pretty. And instead of a race involving the three men with the eight fastest times in history, the final featured two men with the six fastest times — Bolt and Powell.

“I may have needed more races but I don’t really have any excuses,” Gay said. “I just didn’t make it. My hamstring feels good. It’s not bothering me. I wasn’t too overwhelmed with it being the Olympics. It just was one of those things that happened. Maybe I could have used some more training or more races.”