BEIJING (AP) -Kristin Armstrong won the gold medal Wednesday in the women's time trial, making her just the second American women's cyclist to become an Olympic champion.

Armstrong finished the 23.5-kilometer (14.6-mile) course in 34 minutes, 51.72 seconds - 24.29 seconds better than Emma Pooley of Britain. Karin Thuerig of Switzerland was third, almost a minute behind Armstrong.

Pooley was the fifth of 25 riders down the ramp, setting a time that let the other contenders know what they needed.

Armstrong was the only woman close to Pooley at the halfway mark, and erased the gap before reaching the finish at the Great Wall. She joins Connie Carpenter-Phinney as the only American woman to win Olympic cycling gold. Carpenter won the road race at Los Angeles 24 years ago.

"It's the most amazing day of my life,'' Armstrong said. "I've been working for this for the last eight years, especially the last four, and to time everything right on one day is an accomplishment of its own.''

Minutes later, she wrapped her arms around her husband, crying the happiest tears she'd ever shed.

"The moment that I had today, it's one of those dreams you have as a child in America,'' Armstrong said.

Armstrong could barely contain her glee as she stepped atop the medal podium, thrust her arms in the air and then bowed to have Olympic gold draped around her neck.

"Awesome,'' she said. "Just awesome.''

She's the third straight American to medal in the women's time trial, joining Dede Barry and Mari Holden, who won silvers in Athens and Sydney, respectively.

"I am thrilled for Kristin,'' Barry said from Spain, where she now makes her year-round home. "She did a fantastic ride.''

Jeannie Longo of France, competing in her seventh Olympics at the age of 49, took fourth place.

"After the road race I was absolutely exhausted,'' Longo said. "I wasn't like normal. I had problems with my left leg.''

Pooley supported teammate Nicole Cooke to victory in the road race on Sunday, but this race was hers.

"In the road race, I was doing my job. Today, I just concentrated on riding as fast as I could, being absolutely smooth and enjoying myself without anyone to push me off,'' she said.

Christine Thorburn of the United States, who was fourth in the time trial at the 2004 Athens Games, finished fifth but was only 3.17 seconds off Thuerig's bronze time, and lamented afterward not knowing she was so close because the radio feeding her split times had shorted out during the race.

Nonetheless, she was thrilled to see her American teammate kiss the gold.

"I'm so happy for Kristin,'' Thorburn said. "She's been preparing impeccably for the last four years, frankly. She was totally ready and totally deserving.''

It completes a stirring cycle for Armstrong, who turned to cycling only after arthritis in her hips forced her to abandon a career as a professional triathlete. She made the 2004 Olympic team, but was left off the two-woman roster for the time trial in Athens, a decision that pained her deeply.

In the end, it worked out perfectly.

And now, maybe she'll stop being asked if she's related to that OTHER Armstrong, the one named Lance who has seven Tour de France championships on his resume. (They're not related.) She one-upped Lance on Wednesday - his best Olympic finish was a bronze.

"I've tried to enjoy every bit of this whole journey,'' Armstrong said. "But today, today was the ultimate.''

She won the bronze medal at the world championships in 2005, then was the gold medalist a year later, when she truly began believing she could find her way to the medal stand in Beijing. Armstrong was the silver medalist at last year's world championships, saying that defeat wound up motivating her even more for this race.

"It's the most amazing day of my life,'' Armstrong said. "I've been working for this for the last eight years, especially the last four, and to time everything right on one day is an accomplishment of its own.''

Marianne Vos of the Netherlands, one of the medal hopefuls, had a bad day, coming in 14th more than two minutes back, missing out on a medal for the second time after her sixth place in the road race. She fell to the floor after the finish line, exhausted.

"I gave everything. It just wasn't good enough,'' Vos said.

Vos has one final hope of gold, in the points race on the track.

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Associated Press writer Naomi Koppel contributed to this report.