Yost characterized it as a one-day break from the lineup, letting his two slumping and left-handed-hitting regulars sit out while the Athletics started a left-hander, Tommy Milone, in the series opener.
Gordon pinch-hit for Jason Bourgeois to lead off the ninth -- striking out against A's closer Grant Balfour, who got the save in a 1-0 Oakland win.
Gordon and Moustakas likely will be back in the starting lineup on Tuesday night against A's right-hander Graham Godfrey.
"I can almost guarantee it," Yost said. "I've got 25 guys on this team. Everybody's got to play. I've got to get everybody at-bats when I can and the only time I can get the [reserve] outfielders their at-bats is if one of the other outfielders is really struggling."
Bourgeois, who didn't play as the Royals won two of three games at Anaheim, replaced Gordon in left field and the leadoff spot on Monday. Yuniesky Betancourt took over for Moustakas at third base and batted sixth. Both Bourgeois and Betancourt bat right-handed.
Gordon was 0-for-13 with six strikeouts in the three games against the Angels and Moustakas was 1-for-11 (a home run) with four strikeouts.
"Both of those guys are really close to putting it together," Yost said. "They haven't had a lot of luck, Moose especially. It's not like we're putting them on the bench [Monday] because they can't handle lefties, it's mostly getting Bourgeois in there and we'll look sometime in the next two days to get Mitch [Maier] in a game."
Center fielder Lorenzo Cain, a right-handed batter, also was 1-for-11 at Anaheim. Maier gives Yost a left-handed alternative.
Chris Getz, off to a 3-for-5 start, was at second base on Monday night with Betancourt moving to third.
"It's left on left [Monday], so get Yuni over at third," Moustakas said. "Getzy hit the ball real well [Sunday] so keep him in there, give me a nice little day off and get ready to come off the bench later on today."
Gordon hit .366 in Spring Training with four homers and 14 RBIs in 25 games.
"No one wants to be out of there, everyone wants to play," Gordon said. "Obviously I want to be in the lineup, but Ned knows what he's doing so it's his call."
Gordon was used as a pinch-hitter for Bourgeois in the ninth inning of Monday night's 1-0 loss against right-hander Grant Balfour. He struck out.