Bowker hit two homers, including a grand slam, and drove in seven runs Wednesday night and a San Francisco split squad defeated a Kansas City Royals split squad 7-0.
Bowker tops the majors with 18 RBIs in the spring.
"I knew I had 18, but I didn't know it was leading spring training," Bowker said. "I feel pretty good right now, but I'm still not where I want to be. Definitely in the last week, I've been feeling a lot more comfortable at the plate, seeing the ball a lot better."
Bowker's grand slam came in the sixth off Brad Thompson. Bowker hit a solo homer in the fourth off starter Kyle Farnsworth. Bowker also hit a double in the second inning that scored Buster Posey and Travis Ishikawa.
"I'm trying to do what I can, drive in some runs," Bowker said. "What I want to do is just hit with guys in scoring position. That's like the most important thing."
Bowker, who hit .194 with two home runs and seven RBIs in 31 games last season with San Francisco, is trying to win a job as a backup outfielder and first baseman. While with Triple-A Fresno, he hit .342 with 21 home runs in 104 games.
"He did all the damage," Giants manager Bruce Bochy said. "It was certainly a great day for Johnny. We know Johnny can hit. He's a great bat. It's just a matter of what's going to fit the best for this ballclub. He certainly had a great year last year.
"You like the way the ball jumps off his bat, the power, but there are other things you do have to consider. He's doing all he can do and that's come out and perform well. A lot of factors go into when you're picking the 25 guys that break camp with you."
Posey went 2 for 3, raising his average to .400 in 15 games, and was hit by a pitch before Bowker's grand slam.
Farnsworth, who entered spring training as a Royals rotation candidate after not starting since 2000 with the Chicago Cubs, struck out eight and walked none in throwing 70 pitches in five innings. He gave up three runs and four hits.
Henry Sosa and five Giants relievers combined to shut out the Royals on four singles.
The Giants used three consecutive relievers who were former Royals -- Horacio Ramirez, Tony Pena Jr. and Denny Bautista. The three combined to throw five scoreless innings, allowing three hits, striking out four and walking none.
3B Alex Gordon, who broke his right thumb March 6, will not be on the Royals' opening day roster. "That's official," Royals manager Trey Hillman said. "It's not going to happen." ... Giants 3B Kevin Frandsen left in the ninth after fouling a ball off his face. "He busted his lip up pretty good and was bleeding profusely, so we got him out of there," Bochy said. ... SS Yuniesky Betancourt, who defected in 2005 from Cuba, will leave the Royals Thursday to attend to citizenship matters in Miami. ... OF Brian Anderson was scratched Thursday and given the day off for what Hillman called "a personal matter."