Both pitched one inning in the game, with Hultzen allowing one run on three hits with one strikeout in the third and Walker compiling a scoreless seventh frame with one hit allowed and one strikeout.
"She was like my best friend growing up," said Walker, just 19. "She's still my best friend. Just for her to be a part of all of us is so special. She's helped me a lot, she's given me so much confidence and has always supported me, so having her here has been a great blessing, and I'm very proud that she's my mom and she's here."
In support of his mother, Walker custom-designed the cleats he donned in Sunday's game to include pink ribbons that symbolize the fight against breast cancer. It was the least he could do, he said, to honor his biggest fan -- the woman who raised him and his three siblings on her own, who was there beside him on Draft day two years ago when the Mariners selected him with the 43rd overall pick in the first round of the First-Year Player Draft.
Nellie didn't miss one of Walker's high school games, yet Sunday's prestigious contest represented the first professional game she's seen live. Normally, she watches his games from her computer in upstate New York.
"When I sent her a picture of the cleats, she said she cried," he said. "She said she had no words to describe how she felt. I thought this was the perfect opportunity to be able to support her on a big stage like this. I want her to know that I'm here for whatever she needs, and that everything is going to be all right and I'm here to support her."
Walker and Hultzen were among 10 pitchers on the U.S. team for Sunday's game, which annually features the country's top Minor League prospects.
Hultzen, 22, was the second overall pick in the first round of the 2011 First-Year Player Draft. The left-hander thrived at the Double-A level at season's start, gathering an 8-3 ledger with a 1.19 ERA and 79 strikeouts in 75 1/3 innings, before earning a promotion to Triple-A Tacoma in late June. He's 1-1 with a 5.25 ERA in three starts there and is expected to make his big league debut by year's end.
The lefty doesn't have a personal timetable for his anticipated callup, though.
"I really don't want to get too ahead of myself," he said. "I'm just enjoying the experience."
So, too, is Walker, despite his recent woes, which he feels he can soon be wiped away with continued improvement on his secondary pitches.
"It's been tough, but I feel like I've done a pretty good job so far," he said. "It's not going to get easier, so I think if I stay confident and positive I can work through it. The hitters here are really good, so you're forced to become more of a complete pitcher. I've had to show offspeed more, and I'm feeling more confident each time out.
"Being here, it goes a long way with your confidence. Just being here is such a great experience, for me and my mom. Who knows? Next year, she might not be able to come out and watch a game live. So I'm going to enjoy this with her while I can."