By Mark Bendeich and Mark Trevelyan

RIO DE JANEIRO (Reuters) - Gregorio Paltrinieri of Italy won the Olympic gold medal in the 1,500 meters freestyle on Saturday after dominating throughout the race with a relentless display of technique and endurance in the longest event in the pool.

Connor Jaeger of the United States took the silver, and Italy's Gabriele Detti won bronze after overhauling Jordan Wilimovsky of the U.S. in the closing stages. But the winner never seemed in doubt after world champion Paltrinieri took the lead at 150 meters and wore down the rest of the field.

"It's incredible. Really. I have been dreaming of this moment since I was a child and it's amazing," the 21-year-old said.

"There was a lot of pressure on my shoulders. Italian people really wanted this gold and it was more difficult than I expected."

Having been on track through most of the race to beat the world record, he eased off slightly to clock 14 minutes, 34.57 seconds, 3.55 seconds outside the mark of 14:31.02 set by Chinese swimmer Sun Yang in London in 2012.

The winning margin was 4.91 seconds.

"At a certain point he just took off and I thought maybe I could try to hang with him but I couldn't," silver medalist Jaeger said.

"And then you have to hope -'Like man, I hope he is going fast, because otherwise I am really going pretty slow.'"

Breathing to the right after each powerful stroke, the Italian had stretched his lead to more than two seconds by 350 meters and more than three by 550, as Australia's Mack Horton and Jaeger led the chasing group early on.

Wilimovsky had moved up to second by 650 meters and it looked as though he and Jaeger would claim the other two medals.

Detti, the bronze medalist in the 400 freestyle on the first day of competition, caught Wilimovsky shortly after 1,300 and held on to take the bronze.

Australian Horton, gold medalist at 400, finished fifth, and Canadian Ryan Cochrane, silver medalist in 2012 and third in 2008, came sixth.

"Usually I am the one who goes out fast, so that's kind of when I knew I was in a bit of trouble – when he was able to go out faster than I was," Horton said of Paltrinieri.

"I tried to stick to Connor but I just couldn't."

London champion Sun failed to make the final after finishing 16th in the heats.

(Editing by Greg Stutchbury)