The American BMC Racing rider held off Spain's Team Sky rival Mikel Landa in a two way sprint at the end of stage 18 in the Dolomites.

It came after he decided to focus on winning individual stages rather than the overall title after losing contact with the overall contenders last week.

He attacked early on in the 137 kilometres stage from Moena to Ortisei.

After a series of surges, only van Garderen and Landa remained at the front as the race entered the finishing straight.

Van Garderen edged ahead to win in 3 hours 54min 3sec to claim a first American win in a Giro d'Italia mountain stage since Andy Hampsten in 1988.

He had never won an individual Grand Tour stage before, but did form part of winning team time trials for BMC at the 2015 Tour de France and Vuelta a España.

Thibaut Pinot of France and FDJ finished third on the day, eight seconds back to move fourth overall.

"Tejay did well," said BMC Racing sport director Max Sciandri. 

"He showed that the condition is there, and it was a good day out there for him."

Tom Dumoulin finished in ninth place to maintain his overall lead.

The Dutch Team Sunweb rider finished alongside closest rival, Colombian Movistar Team rider Nairo Quintana, to remain 31 seconds clear.

Vincenzo Nibali sits third, 1:12 behind the winner, with Pinot a further 24 seconds back.