Their 2-1 victory gave Finland - who won the inaugural Nations Cup tournament in 1999 - the trophy for the second time.
Due to wet weather that left the track with an ultra-slippery surface, the final of the Nations' Cup was reduced from five heats to three.
That did not seem to make a difference to Renault Formula One driver Kovalainen though, who took an easy win in the first heat in Renault Meganes when the USA's representative Travis Pastrana put the power down too hard at the track's fastest corner and spun off.
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The undoubted highlight though was the second heat when Pastrana - who was competing on his own after his team-mate Scott Speed was injured on Thursday - took on Gronholm in Citroen Xsaras.
Gronholm - a double world rally champion - seemed to throw away Finland's victory chances when he stalled on the start line, but was allowed back into the heat when Pastrana ran wide and into the barrier two corners later.
But the Finn saw his fightback come to nothing when he clobbered the barriers hard on the final lap - forcing the marshals to replace them before the final run-off and ensuring that Pastrana claimed the win.
That brought everything down to a final face-off in buggys, but Kovalainen made no mistakes in an uneventful heat that saw Finland claim a routine win - one that gave them the title.
USA 2-1 Scotland
Pastrana did not look like making the final after spinning his Renault Megane in the opening heat of his semi.
After spending a minute stationary, he got his car back in a straight line just as opponent David Coulthard was about to lap him, causing the Scot to momentarily stall as well.
A switch to Citroen Xsara rally cars in heat two saw Pastrana beat Colin McRae after the 1995 WRC champion used too much handbrake at turn two and clattered the barriers, and a final win against Coulthard in Buggys sent the USA through.
Finland 2-1 France 'A'
Sebastien Loeb showed just why he is the world's top rally driver as he beat his WRC title rival Marcus Gronholm in his familiar Citroen Xsara in heat two to set-up a mouthwatering final face-off.
He needed too as well after his countryman Sebastien Bourdais threw away the first heat when he understeered off and beached his Renault Megane in the sand on the second lap, surrendering the win to Heikki Kovalainen.
Surprisingly, it was Bourdais, and not Loeb, who was selected for the final heat in buggys, and it proved to be the wrong decision as Kovalainen beat the Frenchman easily.
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