By Scott Malone

RIO DE JANEIRO (Reuters) - Kenya's Eliud Kipchoge won the men's Olympic marathon with a dominating performance, running alone into the Sambadrome and finishing in two hours, eight minutes and 44 seconds on Sunday.

Ethiopia's Feyisa Lilesa claimed the silver medal and American Galen Rupp took the bronze in humid conditions on a rain-slicked course.

Kipchoge, 31, began to split the field after around 30 kilometers, starting with a group of a dozen runners about him that slowly dropped away until he ran the final kilometers alone.

"It was a bit slow so I decided to take over. Maybe it was the rain, maybe not. Everyone wants a medal. I was coming here for gold," said Kipchoge, who has won seven of the eight marathons he has entered, including two London Marathon victories.

In previous Olympic appearances, in 2004 and 2008, he had competed in the 5,000 meters before shifting his focus to the longer distance.

Rupp, 30, also made the transition from a short event but did so at the same Games, having finished fifth in the men's 10,000 meters eight days ago.

"I was emotionally drained after the 10K, but I got it out of the system and decided to have an attacking race," Rupp said. "Maybe this is my best event."

It marked the third straight time a Kenyan had claimed a spot on the Olympic podium, following silver and bronze performances in 2012 and a 2008 gold.

As he crossed the line, Lilesa raised his crossed arms in the air, a gesture of solidarity with members of his tribe who have faced violent government reprisals to their protests against a plan to redevelop farmland. [L1N1B20E5]

Kipchoge's victory came a week after compatriot Jemima Jelagat Sumgong won gold in the women's marathon, marking the first time both races had been won by the same nation.

Sunday's race was relatively slow for a world-class marathon, which several runners blamed on the wet conditions. But Kipchoge said he aspired to eventually break the marathon world record of 2:02:57, set by countryman Dennis Kimetto in 2014.

"It is at the back of my mind, but I cannot say when," Kipchoge said. "But I want to cap my career with a world record, yes."

Rupp tipped his hat to the victorious Kenyan.

"It's not like he's a one-hit wonder where he ran one great race," Rupp said. "He's done it over and over and over again."

(Additional reporting by Isaack Omulo; editing by Ken Ferris, Brian Homewood and Bill Rigby)