American Greg Hancock won the Speedway Grand Prix in front of more than 50,000 fans at Cardiff's Millennium Stadium.
The Californian saw off the challenge of Britain's Tai Woffinden, Australian Darcy Ward and Poland's Krzysztof Kasprzak in the final.
But the 44-year-old saw Woffinden move three points ahead of him in the overall World Championship standings.
Defending champion Woffinden, 23, picked up 18 points from the heats and the final, to Hancock's 14.
There are five rounds of the championship remaining.
It was Hancock's third win under the closed roof at the Millennium Stadium, and he described the atmosphere as "hair-raising".
"I've had three wins here now and every one of them has been insane. The noise and atmosphere here is unbelievable," he said.
"It's hair-raising to hear that crowd go off."
Hancock added that consistency through all the rounds is the key to winning the world title.
"Winning finals isn't always the key to winning the title," he said.
"It's about getting the points in the heats as well as winning the finals. You can miss out on the final and still get more points than the rest."