Castillo didn't have to. Baez hit a walk-off two-run homer, his second blast of the game, to lift the split-squad Cubs to a 7-5 victory over Japan in an exhibition game in front of 2,915 at HoHoKam Stadium.
Baez also hit a solo shot in the seventh, which closed the gap to 5-4, and the Cubs tied the game in the eighth on Dan Vogelbach's RBI single.
The Japanese team may have been a little jet-lagged. They arrived in Arizona late Tuesday, and played the Giants on Thursday. The next stop is San Francisco for the semifinals of the World Baseball Classic.
"It was a real baseball game -- it wasn't really a Spring Training baseball game," Cubs bench coach Jamie Quirk said of the close contest.
Baez, the Cubs' No. 1 Draft pick in 2011 and the club's No. 1 prospect, said the last walk-off home run he could remember came in high school.
"[The first homer,] I was just sitting on a fastball, and he threw me two, and I missed them, and then he threw me a fastball inside," Baez said. "I was patient at the plate. [In the ninth], with a man on second, I knew he'd throw a slider or a curveball, and he threw me a slider and I hit it hard and hit it over the fence."
This was Baez's third spring home run, although the statistics from the exhibition game won't count in the Cactus League stats.
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.