Australia's Sally Pearson took 100m hurdles gold from reigning champion Dawn Harper with a new Olympic record of 12.35 seconds.
Pearson went one better than her silver in Beijing and celebrated wildly as replays on the stadium's big screen confirmed that she had held off her American rival by just 0.02 secs.
It was a new personal best for Harper and also for Kellie Wells in bronze with 12.48secs, despite a slight headwind of 0.2ms.
Pearson had been beaten by Wells in London last month but came into these Games as favourite after winning world gold a year ago in the middle of a long unbeaten run.
A beautiful hurdler, she also has the nerveless temperament needed on these big occasions.
"I don't even know how to describe it, it's a dream," she told BBC Sport. "Relief was the first thing I felt and then shock.
"I really wanted this tonight. I've worked so hard to get this."
It is Australia's first track and field gold of the 2012 Olympics and, after her compatriot Anna Meares beat Vicky Pendleton in the velodrome across the park a few hours earlier, made it a golden few hours for the country's preeminent sprint athletes.