Michael Weaver opened a big lead and hung on to beat Justin Thomas 3-and-2 Saturday to advance to the final of the U.S. Amateur championship at the Cherry Hills Country Club.

Weaver will face Steven Fox of Hendersonville, Tenn., in Sunday's 36-hole match-play championship. Fox won his semifinal 2-up over Brandon Hagy, who is Weaver's teammate at the University of California at Berkeley.

The 21-year-old Weaver, of Fresno, Calif., opened his semifinal match with Thomas with three consecutive birdies to go 2 up. He stretched his lead to 5 up after the 10th hole and withstood a rally by Thomas, an Alabama freshman who won three of four holes to get within two of Weaver.

"The start was incredible, awesome," Weaver said. "I just kept hitting good shots and kept giving myself chances. That really helped me out a lot because I needed it. Justin came around a little bit and I slipped a little bit. But to start like that in the biggest match I've ever played in, that was an awesome feeling."

Weaver secured the win when he knocked in a 6-foot birdie putt on the par-4, 451-yard 16th hole as Thomas just missed a 15-foot birdie putt.

He thrust his arms in the air in celebration and got a hug from his father, Bill Weaver, who has caddied for his son throughout the weeklong tournament. Both wiped away tears of joy.

"I'm so proud of him," Bill Weaver said. "He's a very strong individual, no give-up in him. He just gutted it out."

Michael Weaver got choked up again later, recalling his clinching putt to get to the championship round and sharing it with his father.

"That was pretty special," he said. "I'll remember that forever. I'm so excited. My dad caddies for me all the time. I'm so excited he could be here to be part of this. I owe him a lot. He's supported me all along, everything I needed and I wouldn't be here without him."

Thomas said Weaver simply outplayed him on the front nine and the deficit proved too much to overcome.

"I didn't battle through it well enough," Thomas said. "Although it hurts a lot to lose, especially this late in the tournament, it's a lot better to get beat than to lose."

The championship on Sunday brings together two longshots from an original field of 312 golfers from 43 states and 20 countries that began the stroke play qualifying on Monday. Both Fox and Weaver emerged from a playoff at the end of two days of qualifying to win their respective spots in the 64-player match-play field. Fox was the No. 63 seed and Weaver the No. 60 seed.

Along the way, Weaver had to get past Thomas, the Jack Nicklaus award winner as the nation's top college golfer. Fox advanced to the semifinals by defeating Chris Williams, the University of Washington star who was the top-ranked amateur.

"Whether you're No. 1 or 64, you always have a chance," Fox said. "And it's awesome how we survived a playoff and got this far. It's really unreal."

On Saturday, Fox weathered a tightly contested match with Hagy that was all square as late as the 14th hole. Fox made par on No. 15, and went 1 up when Hagy missed a 10-foot putt for a bogey.

They matched each other on the next two holes. On the par-4, 472-yard 18th hole, Fox used a 4-iron to drive his second shot 206 yards, landing it within 6 feet of the hole.

"Best shot of my life," Fox said.

It also impressed Hagy.

"That was a spectacular shot," Hagy said. "Very clutch. And my shot, I hit it right at the flag. It looked really good and just went a little too far."

Hagy overshot the hole on his second shot, rolling the ball to the back of the green. His try for a long birdie putt was wide, and it gave Fox, a senior at Tennessee-Chattanooga, the 2-up victory.

Then his phone started ringing.

"It's been going off like crazy," Fox said. "There's so many people back home backing me. I mean, it's just awesome. Without them I wouldn't be here, especially my family. They're all rooting for me. It's an unbelievable feeling. It just puts a smile on your face."