Kristin Armstrong won her second consecutive gold medal in the Olympic women's time trial on Wednesday morning, besting a field of 23 other riders in London.

Armstrong, a Boise resident and University of Idaho graduate, completed the 18-mile course in 37 minutes, 34.82 seconds, well ahead of second-place finisher Judith Arndt of Germany, 37:50.29. Olga Zabelinskaya of Russia finished third.

The City of Boise announced a community-wide celebration for Armstrong on Aug. 11, her 39th birthday. Details are still to be announced.

Armstrong won the gold in Beijing in 2008. She retired in 2009 and gave birth to son Lucas in Sept. 2010. She returned to racing in 2011 with the goal of winning gold in London. The 38-year-old completed her goal despite fracturing her left clavicle in a crash at the Exergy Tour in Idaho in May.

Armstrong crashed in Sunday's road race as well, suffering minor injuries to her left elbow.

But nothing could stop her Wednesday.

Armstrong led the race at the first interval (5.6 miles) by 1.5 seconds and at the second interval (12 miles) by five seconds and extended that lead on the way to the finish line. There was little drama as she approached the end, having passed road race gold medalist Marianne Vos, who started three minutes before her, on the course.

"To come back as a mom and win a gold medal a second time is a dream come true," Armstrong said after the race, according to USA Cycling.

Armstrong said she had some doubts in the days between her road race crash and Wednesday's time trial. But said the thought of living with this result forever pushed her forward.

"Whatever I do today is what I get to look back on in my career," Armstrong told NBC after the race.

The famously stoic Armstrong let a smile slip as she crossed the finish line, slowing to a stop and then slumping over her bike. She rested just enough to catch her breath before heading to the victory stand and her second consecutive Olympic gold.

"When she stopped, she was on top. You don't lose what you've got," said Armstrong's American teammate Amber Neben, who finished seventh. "You don't lose the fact that you're a great bike racer."

The mostly flat course that Armstrong turned into her own personal playground began at Hampton Court Palace, the 16th century court that was once favored by Henry VIII.

The race meandered through countryside, twice crossing the River Thames, before finishing back at the palace. Riders who were in position to medal were ushered onto so-called hot seats - three gilded thrones - to wait out the rest of the riders.

Armstrong said, in a post-race interview with NBC, that she didn't know for sure she had won.

"I didn't know until I had crossed the finish line," she said. "The information I was getting was it was a close race out there and that I needed to give everything I had if I wanted it. I knew just one percent off the pedals is going to take you to second or third or even off the podium."

She becomes the oldest champion in a road cycling event. Armstrong turns 39 on Aug. 11.

"I don’t want to do anything less than gold. It'd be one thing if I got silver or bronze the last time around. One more higher medal would be good. But it's hard going in as defending champion and thinking you want anything less than a win," Armstrong told the Statesman before the Games.

Armstrong battled back tears before she was given the gold medal on the podium. She asked if her son Lucas could be on the podium with her. An Olympic official said, "I don't think so." After the ceremony, Armstrong held Lucas on the stage. He held flowers. She held her gold medal.

"The reason I came back was because of the feeling I got back in Beijing on the top step. But I couldn't imagine anything better than being on the top step with my son Lucas," Armstrong told NBC.

Armstrong's husband, Joe Savola, got choked up when talking about seeing his wife and their son on the podium with the gold medal.

"Honestly, that was the dream," he said. "That was the whole dream. That's what we wanted to do."

Armstrong was among the favorites in the race, which also includes former world champions Neben, Emma Pooley (Great Britain) and Judith Arndt (Germany) and Linda Melanie Villumsen (New Zealand), who finished second in the 2011 world championship and third in 2010.

Seven riders in the time trial competed in May’s Exergy Tour in Idaho — Armstrong, Neben, Canada’s Clara Hughes and Denise Ramsden, Sweden’s Emilia Fahlin, Germany’s Trixi Worrack and Australia’s Shara Gillow.

Armstrong said before the London Games that this was her final season and there was no chance that she would compete in the 2016 Games in Brazil. Armstrong said earlier this week that she expects to return to Boise on Friday.

She told NBC after the race, "I'm officially retired."