Australia's Anna Meares stunned Great Britain rival Victoria Pendleton to win gold in the women's sprint at the London 2012 Olympic Games.
This is the sweetest and most incredible victory of my career.
China's Guo Shuang took the bronze after beating Kristina Vogel of Germany in the race for third place.
Pendleton, racing for the last time in what has been a hugely successful career, had been expected to beat her arch-rival after showing stunning form on the way to the final.
However, the 31-year-old Englishwoman's nerve seemed to go after she was relegated from the first race, which she won on a photo finish, having made the critical error of coming out of her sprint lane.
"I was really annoyed because I'm sure that she touched me and it caused me to move up," Pendleton said.
"I can't believe, twice in one competition, I've been disqualified and relegated, it's unheard of. It's a bit of a surprise, it did knock my confidence a bit I must say."
The pair got up for the second race, but after Pendleton took the race by the scruff of the neck, after a brief trackstand, she had no response when Meares put in a big turn of pace on the back home straight.
Meares won with relative ease at the finish where she pumped the air in joy.
"This is the sweetest and most incredible victory of my career," said Meares
"Victoria's such a hard-fought opponent and she's dominated the sport for so long," Meares said.
"It's been such a difficult challenge and to be able to win the Olympic title for me, it's so special.
"I've tried so much and worked so hard for a long period of time and I've asked a lot of people around me to do the same so it feels like this is a just reward."
It is Meares's second Olympic title, but first in the sprint, in which she finished behind Pendleton in 2008. Meares won the 500m time trial gold at the Athens Games in 2004.
Pendleton had come to her final Games having set a series of personal bests at a recent squad training camp in Newport, Wales and continued that form during six days of competition in which Great Britain blew its rivals away on the boards.
Crowned keirin champion on Friday, she began her campaign by posting a new Olympic record of 10.724sec for the 200m flying lap, the opening salvo in the demanding, three-day battle for the sprint title.
But as Pendleton was beating all her match rivals, from Russia teenager Ekaterina Gnidenko, to Netherlands rider Willy Kanis through to Belarus's Olga Panarina and then Vogel in the semis, Meares was going about her business in the same fashion.
The Australian was the only other rider to post a sub-11 second time in qualifying.
She then coasted past Kayono Maeda of Japan, Canada's Monique Sullivan, Ukraine's Lyubov Shulika and showed similar class in disposing of Guo 2-0 in her semi-final matches.
Gold medal sprint race 1
1 Anna Meares (AUS)
2 Victoria Pendleton (GBR) REL
Gold medal sprint race 2
1 Anna Meares (AUS) 0:00:11.348
2 Victoria Pendleton (GBR)
Bronze medal sprint race 1
3 Guo Shuang (CHN) 0:00:11.532
4 Kristina Vogel (GGER)
Bronze medal sprint race 2
3 Guo Shuang (CHN) 0:00:11.591
4 Kristina Vogel (GER)