LONDON — Allyson Felix won her second Olympic gold medal at the London Games and added a world record for good measure as she helped the U.S. relay team power past its Jamaican rivals in the 4×100 meters.

The 200-meter champion ran a blistering second leg and 100-meter silver medalist Camelita Jeter finished off the world record performance, pointing to the time clock with her mouth wide open as soon as she got past the finish line, seeing that the 27-year-old mark of the former East Germany was gone.

The U.S. team finished in 40.82 seconds, shaving a massive 0.55 seconds off the old mark.

“To look up and see we had a world record, it was just crazy,” Felix said. “I didn’t think that was going to happen.”

Jeter knew she was shooting for the world record as she was dashing down the home stretch, Jamaica already well beaten.

“As I’m running, I’m looking at the clock and seeing this time that’s like 37, 38, 39. In my heart I said, ‘We just did it!’” Jeter said.

It was the second world record in as many days on the super-fast track at the Olympic Stadium after David Rudisha of Kenya set a fresh mark 800 on Thursday night.

Now, Felix will bid for a third gold medal if she runs — as expected — in the final of the 4×400 relay on Saturday.

Almost as amazing as the U.S. women’s 4×100 relay record was the stunning loss by the U.S. men’s 4×400 relay after it had won every Olympic gold medal in the event since boycotting the 1980 Moscow Games.

In a thrilling finish, Ramon Miller of the Bahamas chased down and swept past Angelo Taylor in the final straight to deprive the United States of a gold it long thought it had a lock on.

“I tried to kick and come home. Unfortunately, Ramon had more than I did,” said Taylor, a two-time Olympic champion in the 400-meter hurdles.

Such was the surprise that it overshadowed Oscar Pistorius’ last race at the London Games. Pistorius, known as the “Blade Runner,” got the South African baton in last place and crossed the line in eighth in an anticlimactic performance after he had become the first amputee runner in track and field to compete at the Olympics.

“It has been incredible to be here,” said Pistorius, a double amputee who runs with the aid of carbon fiber blades. “Just to participate has been great and now I am really looking forward to the Paralympics.”

One favorite to come through as expected was Renaud Lavillenie of France, who won pole vault gold with an Olympic record jump of 5.97 meters.

Former world-record holder Tatyana Lysenko of Russia, who served a two-year doping ban until 2009, set a games record of 78.18 meters to win the hammer throw.

No one came close to an Olympic record in the 5,000, but Meseret Defar reclaimed the title she first won eight years ago, as her Ethiopian compatriot Tirunesh Dibaba missed a chance to become the first woman to repeat as double Olympic long-distance champion.

Defar swept past the front-running Dibaba in the final straight and had enough power to hold off Vivian Cheruiyot of Kenya. Dibaba, running with blue tape on the back and inside of her right thigh, faded toward the end and was unable to produce the kick that earned her gold in the 10,000 last week.

Once she crossed the line, Defar produced a religious image of a virgin and child to show to the cameras before breaking down, sobbing into the picture.

After she won at the 2004 Athens Games, Defar has often had to spend time running in the shadow of Dibaba. Now the two have combined to dominate their fierce rivals from Kenya over the long distance events in London.

“I feel like I’ve been born again,” Defar said. “After eight years, to get gold again is big.”

Ethiopia had already won the women’s marathon in the center of the city last Sunday, and the favored Cheruiyot failed to even get close to her world championship double from last year.

Dibaba was one race away from achieving the long-distance equivalent of what Usain Bolt did over the sprints on Thursday.

Bolt’s double in the 100 and 200 turned him into a self-proclaimed “living legend,” and he rested on Friday while his 4×100 relay teammates toiled.

The Jamaican relay team still easily qualified for Saturday’s final in 37.39 seconds, the fourth-fastest time in history at that stage. Then the U.S. team trumped them with 37.38 seconds for a U.S. record.

On Saturday, Bolt will have chance to show if he can make enough of a difference on the fast track to produce another world record in the finale of the weeklong U.S-Jamaican battle for sprint supremacy.

Alsi Cakir Alptekin led Gamze Bulut in a 1-2 finish for Turkey in the 1,500 final. Two-time world champion Maryam Jamal of Bahrain took bronze.

U.S. runner Morgan Uceny had another tumble at a major meet, crashing to the track at the start of the last lap and failing to finish the final. She was the leading 1,500 runner leading into the world championships last year but fell in the final at Daegu.