Moustakas was the second overall pick in the 2007 first-year player draft. Hosmer went third overall the following year. Together, the third baseman and first baseman were general manager Dayton Moore's cornerstones in his plan to build a contender.
Yet even through this summer, they struggled. Moustakas spent months trying to get his batting average over .200, even getting banished to the minor leagues. Hosmer experienced a power outage, rarely taking a pitch deep.
Perhaps now, they are finally living up to those expectations.
Moustakas hit the go-ahead home run in the 11th inning in Game 1 of their AL Division Series against the Angels. Hosmer hit a two-run shot in the 11th inning the next night. And in the clincher on Sunday night, both of them went deep in an 8-3 victory.
''It's times like this that we've been prepared for, and were preparing for in the minor leagues for a long time,'' said Hosmer, who hit .270 with nine homers in the regular season.
''A big asset or a big characteristic when Dayton drafts guys is character, and I think every single person in that locker room is showing that right now with the way we've been battling back, the way we've been in some holes and we've had our season on the line,'' Hosmer said. ''It's the guys that aren't going to quit, the guys that believe they can do it.''
Guys like Moustakas, whose ability to hit home runs made him too good for the Royals to pass up. He was plucked out of California's Chatsworth High School one pick after Tigers ace David Price, and ahead of future All-Stars Matt Wieters and Jason Heyward.
He made his professional debut at 18. He rocketed through the minor leagues, reaching Triple-A Omaha three years later. And he quickly moved into the starting lineup at third base.
Moustakas hit .263 during his abbreviated rookie season, and the Royals thought they had found the next George Brett - with more power. But the young slugger regressed the next year, hitting just .242, and even hit just .233 in 136 games last year.
Things may have bottomed out earlier this year, when Moustakas was drawing the ire of Royals fans. Many thought he should be released, but the Royals stuck with him.
He's returning their belief in him this postseason.
''We don't really care how we win ballgames, so long as we get a W at the end of the night, and I think I speak for 25 guys in the clubhouse that will say the exact same thing,'' Moustakas said. ''We go out every night with intentions to win.''
Hosmer, who won his first Gold Glove last year, hasn't had nearly as much trouble in his young big league career. But not everything has been as easy as it was during his rookie season with the Royals, when he hit .293 with 19 homers in 128 games.
Hosmer hit just .232 the following year, his swing utterly abandoning him.
He bounced back last year, hitting .302 with a career-high 79 RBIs. And while he has continued to put the ball in play this season, Hosmer's power numbers have been way down - at least, until the start of the playoffs. Now, he's swinging for the fences again.
''Moose and I, we're just - we're winners,'' Hosmer said. ''We want to win. That's all we care about. The numbers, that's for the scoreboard and for the fans to see, but when it all comes down to it, we want to win, and we're going to do anything we can to win.''
That's good enough for manager Ned Yost, who has stuck by both of his cornerstones.
''We've always believed in Eric Hosmer. We've believed in Mike Moustakas and everybody we've got on our team,'' Yost said. ''I wouldn't say we're sitting back saying, `We told you so.' We're just happy for them that they've put us in position to win baseball games.''