KANSAS CITY -- Kila Ka'aihue is now the A's starting first baseman. It's a job he was projected to have for Oakland's weekend opponent: the Royals.

Ka'aihue was once one of Kansas City's highest-rated prospects, a home run machine in the Minors. He crushed 37 long balls between two teams in 2008 and mashed another 52 over parts of three seasons at Triple-A Omaha. Hype followed Ka'aihue to the big leagues, but he couldn't find his hitting stroke once he got there and was traded to the A's last season after being supplanted at first base by another top prospect, Eric Hosmer.

A season later, Ka'aihue is now getting the opportunity to play at first base on a regular basis in Oakland. Preseason competitors Brandon Allen and Daric Barton are no longer on the roster, leaving regular playing time for Ka'aihue, who entered Sunday's series finale batting .231 with three homers and 12 RBIs. He went 0-for-3 with a walk in a 2-0 loss to the Royals.

"Now he's going to get consistent at-bats," manager Bob Melvin said. "I think you'll see his at-bats from game-to-game get better all the way through. Though, to this point in the season, he's done pretty well for us with not consistent at-bats, so you always think that once you start getting consistent at-bats, once you're in there every day, that the at-bats will get better and so will the production."

Ka'aihue said the increased role wouldn't change his approach.

"I've still got to go out there and play and play well," he said. "It could've very easily been me, so it doesn't change anything."

As for being back in Kansas City -- where Ka'aihue hit just .216 with 11 home runs over parts of three seasons -- the first baseman said he's just happy to reunite with his former teammates.

"I played here for a while. It was a lot of fun. I enjoyed myself here," Ka'aihue said. "I enjoyed the guys that I played with over there. More than anything, I was happy to see a bunch of them. Those are a lot of my good friends, and to come back and see them, that was the biggest thing."

Melvin opts to keep Weeks out of lineup

KANSAS CITY -- A's second baseman Jemile Weeks wasn't in the starting lineup for Sunday's game with the Royals after sustaining a strained left hip in the previous game.

Weeks left in the top of the seventh inning of Saturday's 9-3 win, aggravating his hip trying to steal second base. He was replaced by Adam Rosales, who started at second and batted ninth on Sunday.

After Saturday's game, Weeks said he wasn't worried about the injury, but manager Bob Melvin decided to give Weeks a day off. Weeks did pinch-hit in the ninth inning of Sunday's 2-0 loss, grounding out to Royals closer Jonathan Broxton to end the game.

Weeks has had trouble with his left hip in the past, injuring it multiple times throughout his tenure in the Minor Leagues. Melvin said that was a factor in letting his second baseman rest.

Cespedes back in center for series finale

KANSAS CITY -- Yoenis Cespedes was back in center field on Sunday after starting in left during his first two games back from the disabled list against the Royals.

The change came because manager Bob Melvin wanted to give center fielder Coco Crisp a day off. But Cespedes returned to the position he started every game at prior to his left hand injury.

Cespedes has been challenged early and often in his first stint as the A's left fielder. Melvin spoke about a ball that seemed to fool the outfielder on Friday, and Saturday's game saw a couple of instances that showed Cespedes' newness to the position.

Melvin has said it will take time for Cespedes to get completely comfortable in left, and he reiterated that ahead of Sunday's series finale.

"It's a transition, and when the first ball of the game fools you a little bit, now -- like at any position -- there's some trepidation and you're just not as aggressive and confident with it," Melvin said. "I think the more balls he gets that he reads correctly right away, the more confident he's going to feel. We'll do some stuff at home with balls off the bat, maybe some soft toss stuff where we're trying to direct some balls that have angles to them and so forth, and try to speed up the learning curve."