Left-hander Will Smith had his roughest outing for the Royals, yielding five runs in four innings. Hundley tagged him for his homer in the first inning although all three runs in the inning were unearned.
"It was a first-pitch fastball, I was just trying to get a strike," Smith said. "It was up, belt-high and he did what he was supposed to do with it -- crushed it."
Hundley, who has a .469 (15-for-32) average, boosted his RBI total to seven in 12 games.
"I came in with a lot of confidence with the work I put in the offseason, but it's nice to see the results," Hundley said. "At the same time, if the results weren't there I'd still have confidence in my swing. Results, no doubt, are a nice thing as well."
The Royals' third error, by Smith, also made one of two runs in the third inning unearned.
Behind 5-0, the Royals came back with three runs against Padres starter Jason Marquis in the third inning. David Lough contributed a double, his second hit, and he finished the day with a .548 (17-for-31) average. Lorenzo Cain had a two-run single and Brandon Wood contributed an RBI single.
Luke Hochevar made his first appearance since being switched to the Royals' bullpen on Wednesday and worked two perfect innings.
After Minor Leaguers took over the Royals' lineup, they wiped out the Padres' 5-3 lead by batting around in a four-run eighth inning. Most of the damage came against Tim Stauffer, pitching his third inning. Paulo Orlando started the rally with a double, Alex Llanos belted a two-run double and Angel Franco added a run-scoring single.
"They all did a great job," Royals manager Ned Yost said. "When you give those kids an opportunity, it's big. It's experience for them and to do what they did today was exciting for me. This is as excited as I've been all Spring Training just to see those kids have success and to come back and win a ballgame like that."
Up next: Left-hander Bruce Chen, now positioned as the leading contender for the No. 5 starting job, will make his fourth start at 3:05 p.m. CT on Saturday (live on MLB.TV and a free exclusive royals.com webcast against the Cubs at HoHoKam Park in Mesa, Ariz. He'll also be the first Royals pitcher to bat in a game this spring. Catcher Salvador Perez will get the day off as he concentrates his efforts on catching starters Wade Davis (Friday) and James Shields (Sunday) in Minor League games. Rookie Michael Mariot, who's made a strong impression this spring, will be among the Royals' pitchers. He gave up a three-run homer to the Mariners' Casper Wells but, in his five other innings, Mariot has held opponents to no runs and one hit and been been credited with three saves.