EUGENE, Ore. — Mason Finley established himself as the man to beat in the men’s discus even before Friday’s final round at the U.S. Olympic Track and Field Trials.

The Salida native led the field in qualifying here on Thursday at Hayward Field with the only throw over 200 feet — 218 feet, 11 inches (66.72 meters), a personal best — a mark that made him the fourth-best performer in trials history. Then, as rain threatened during Friday’s final, he refused to let up on the 12-person field, jumping out to the lead with his first throw.

“I’m finally feeling how to throw at that distance,” said Finley, who was surprised by the mark. “Didn’t really get it today, but with the weather adversity, I think I still did pretty good.”

Well, “pretty good” was enough to qualify for the Rio Olympics. In fact, he never relinquished the lead, extending it further with his second throw of 208’1” (63.42 meters). His final throw, a victory lap of sorts, ended up being the second farther of the competition.

“The very last throw, I knew I had won, so it was crazy. But I was thinking I could still throw further,” Finley told The Post. “I wanted 65 (meters) again. … It was a mixture between, ‘I still want to push it further’ but ‘Oh my gosh, I’m an Olympian.’ ”

Finley has lost considerable weight in the last three years. In 2013, he weighed 437 pounds — “I was huge,” he said — and suffered injuries to his back as a result. He couldn’t rotate and turn in a way that would allow him to throw as far as he does now. Today, he competes near 350 pounds, a stunning drop of nearly 90 pounds in roughly three years, the result of studying nutrition more closely and cutting back on carbohydrates. He wants to throw at 330 pounds next year.

“I’m able to hold positions faster, move faster and compete healthier,” Finley said.

Finely attended Salida for two years and then transferred to Buena Vista High School, where he set the national high school record in 236′ 6″ in the event. He originally attended the University of Kansas, competing there for three years, before transferring to the University of Wyoming, where he graduated in 2014 and where his father, Jered, also was a thrower.

After graduating, he went the Olympic Training Center in Chula Vista, Calif., for six months. In February last year, he returned to Lawrence, Kan., to start working with his former throws coach, Andy Kokhanovsky. He also works part-time at GNC and works with local theaters in the area to do behind-stage work.

“I wanted to be closer with my mom and family back there,” Finley said. “I figured out that family is a really huge support staff. You definitely need it.”

Two other Coloradans in the finals field didn’t fare as well. Lance Brooks, who lives in Denver working in construction and assistant coaches at Arapahoe High School, won the trials in 2012, but finished fifth on Friday after throwing 198’6″ (60.5 meters). Colorado Springs native Russ Winger struggled in his first three throws, fouling his first two before getting a mark. He did not make the cut, saying he struggled with soreness and establishing timing. His wife, Kara Winger, will compete Saturday in the women’s javelin final.

Finley — who was competing unattached — was 13th at this meet in 2012 in the preliminary rounds and didn’t even make the final. The last three months, he has been on a tear, progressively throwing farther in almost every meet he has entered.

“I expected a good performance,” he said. “My coach told me, ‘You just have to do the technique.’ That was the main focus, and whatever happened happened.

“It’s definitely time to gear up. That throw (Friday) isn’t going to hold up well in Rio. We gotta put on the afterburners and finish out the season strong.”