Oakland was playing its last game in Arizona before leaving for Tokyo, where the A's meet Seattle in an opening two-game series next Wednesday and Thursday.
"It's just sore right now," Mendoza said. "I was scared because it really hurt. It was a hard ground ball, but it hit my hamstring, it hit muscle in the back of my leg. Right now, I'm glad it's nothing serious. It was a big bruise."
Royals closer Joakim Soria exited Sunday with ligament damage in his elbow. He is taking a few days to consider his options after receiving a second opinion. Soria has damage to the ulnar collateral ligament in his right elbow. He had reconstructive elbow surgery in 2003 to replace the same ligament.
"No more," Mendoza said of pitchers leaving prematurely for the trainer's room.
Mendoza is 4-0 with a 0.77 ERA, giving up one run in 11 2/3 innings this spring.
"The ball got him on the back of the knee, a real meaty part," Royals manager Ned Yost said. "It's just a bruise. It hit him pretty good. It's not something to continue with at this point of the year. You don't want to take a chance of it swelling or him altering his mechanics at all because he's throwing the ball so well."
Yost said Mendoza remains "definitely right in the mix" as a rotation candidate.
Lorenzo Cain, who tops the Cactus League with a .500 batting average, homered to lead off the second inning. Alex Gordon and Eric Hosmer each had two hits and drove in a run for the Royals, who won for the fifth time in six games. Max Ramirez contributed a two-run pinch single in the sixth to up his RBI total to 11 in 13 games.
A's right-hander Graham Godfrey gave up three runs on six hits and two walks in three innings, throwing only 37 strikes in 75 pitches.
"Not very good," Godfrey said of his location. "That's one thing I talked with Curt (Young, pitching coach) about. Typically I fill the zone up, throw a lot of strikes. Today was almost the opposite. It's good to have that kind of outing now, learn from it and make sure that doesn't happen again."
Godfrey was familiar with Cain, who he faced last year when both were in the Pacific Coast League. Cain homered on a 3-1 pitch.
"He's a good hitter," Godfrey said. "This spring he's been doing pretty well. He was one of the guys I had to be careful of last year. It was a case where I was working behind a lot of hitters. I don't want to walk anybody. I gave him a cookie and he did what he's supposed to do with it."
Godfrey worked out of a bases loaded jam in the third, retiring Cain on a fielder's choice to end the inning.
"I thought I made some good pitches when I needed to," Godfrey said. "Sometime it worked out for me. Other times there was a broken bat flare where nobody was playing. I try not to be so result-oriented, but obviously it wasn't the result I wanted, but most of the pitches were kind of where I wanted them. There were some good things and some bad things mixed with a little bad luck I thought."
Minor leaguer Cedric Hunter homered for the A's in the seventh.
A's 3B Scott Sizemore had surgery Wednesday to repair a left knee ligament tear and will miss the season. Sizemore hit 11 home runs with 52 RBIs in 93 games last season with Oakland after being acquired in a trade with Detroit. He injured the knee last month in the A's first full-squad workout. . Yost said C Humberto Quintero and OF Jason Bourgeois, who were scheduled to arrive Wednesday night after being acquired in a trade with Houston, would be in the Royals lineup Thursday.