Moore will take on Luke List, who advanced thanks a 1-up win against Chris Nallen. List held a 2-up advantage with three holes to play, but Nallen tied it up, then ultimately fell.
Immediately after List took the 2-up lead, dangerous weather forced a suspension of play. Moore had already defeated Overton, but List and Nallen waited three and a half hours for play to resume.
Moore was 2-down at one point in his match, but finally took the lead in his match with a 30-foot birdie putt at the 13th. He won the 14th when Overton's pitching-wedge landed on the green, then bounced off the back.
Moore halved the next three holes to advance to his fourth final in a USGA event.
'I can't say I wasn't thinking about it early in the week, what would it be like to get there,' said Moore. 'But, I'm just excited. I'm just glad to give myself a chance to win.'
Moore has been giving himself several chances to win this year. He won the NCAA Individual Championship, the U.S. Amateur Public Links and the Western Amateur this season and now has a 26-4 match-play record in his seven USGA appearances.
'If he goes on to win this, he's basically winning all of the major tournaments in everybody's eyes,' said Overton. 'It's kind of hard to believe, but at the same time, he's basically the only player that has every part of his game going right now. There's not a weakness in his game, and his putting is phenomenal.'
Moore will face a tough test in List, who built a 3-up lead in his match with a par at the eighth. Nallen trimmed the deficit to 1-down, but a List birdie at the 15th gave him a 2-up lead with three to play.
Then came the dangerous weather.
When the players returned, Nallen won the 16th with par, then birdied No. 18 to force extra holes. List birdied the first playoff hole and will get the task of taking on Moore.