JUNO BEACH, Fla. – William Mouw played his first tournament as a kid in gym shorts and high-top basketball shoes. His basketball game had gone long and his dad, Bill, raced his son to the course just in time for his tee time. A 10-year-old Mouw ended up losing in a playoff – to his current Walker Cup teammate Ricky Castillo – proving, even at a young age, that he could handle adversity well.

Now 20 and playing in his first Walker Cup, Mouw again showed his ability to perform on the fly. With U.S. teammate Tyler Strafaci still struggling with a stomach virus that has affected more than half of both teams this week, Mouw was called in as a last-minute replacement and responded with a dominating 4-and-3 victory over Ben Jones on Saturday at Seminole Golf Club.

Mouw’s singles victory was one of five for the American side, which holds a slim 7-5 lead over visiting Great Britain and Ireland at the midway point of the 48^th Walker Cup.

“You go into these fun events thinking, I'm going to play 36 holes for the team,” Mouw said, “and I think just knowing that, you're mentally ready for anything that comes your way.”

Mouw was prepared to spectate on Saturday afternoon after a foursomes loss alongside Stewart Hagestad in the morning. He had his sneakers on and was chatting with his caddie when his phone rang. On the other line was U.S. assistant Robbie Zalzneck.

Hey, Ty’s not doing good. We need you. You ready to go?

Mouw didn’t hesitate: Yeah, I’m ready.

Mouw first rushed to the range to check on Strafaci, who had barely hit six balls before getting sick and retreating to a bench nearby.

“I was seeing two balls when I was standing over the ball,” said Strafaci, one of three players, along with John Pak and Pierceson Coody, who didn’t play foursomes because of illness, but the only one of the three who failed to log action on Day 1.

Medical personnel hooked Strafaci up to an IV at the course, but he was soon transferred to a local hospital for the second time this week for more treatment. He returned to Seminole three hours later with a hospital band on his wrist and some cotton gauze taped to his arm where the IV was hooked up. Just in time, too, to give Mouw a huge bear hug on the 15^th green.

“I wanted to go out and compete,” Strafaci said. “This is what I’ve been preparing my whole life for. It wasn’t easy at all [to make this decision], but physically I couldn’t have walked 18 holes today.”

Added U.S. captain Nathaniel Crosby: “It's very easy to be bravado and you get out there on the third or fourth hole and then you have to come in and you cost your team a point. … He did the right thing. He's really the understated hero pulling himself out and giving William the chance to win the USA a point.”

Mouw had only about 30 minutes to warm up. He hit a few balls, struck a few putts and off he went in the fourth of eight matches out. Two holes in, though, he was already down.

“Man, that first tee shot right off the bat; I got thrown into battle really quick,” Mouw said. “My mind was racing for the first few holes.”

But then the Pepperdine sophomore hit a beautiful 4-iron to 20 feet at the par-5 third hole and sank the putt for eagle, squaring the match and leveling his heart rate.

“That calmed me down,” Mouw said, “and I was in control of the match pretty much the whole time.”

Mouw played his next nine holes in 1 under with two birdies to take a 4-up lead after 12 holes. Three holes later he closed out Jones with bogey at the par-5 15^th hole.

“He struck it so well today,” said Bill Mouw, who then pointed to his ear. “I can still hear the sound.”

Strafaci, who was spotted striking putts on the practice green around 8 p.m. Saturday, likely won't need a sub on Sunday. He said he expects to be ready to go as he plays twice on the final day, in foursomes with Stewart Hagestad and in singles against Jack Dyer. Not that Mouw would be able to sub in again. He'll team with fellow Californian Castillo in foursomes (they'll play Alex Fitzpatrick and Barclay Brown) and then face Angus Flanagan in singles.

Two more opportunities to shine for a guy who's quickly becoming a star for the American side – and not just because of his Taylor Swift rendition earlier in the week.

"He's all upbeat, all positive, California cool, Malibu's Most Wanted," Crosby said playfully. "He's going to have his own cartoon in about a year. This guy is fantastic."

And ready to rock at a moment's notice.