Gennett, who is 5-foot-10 and 166 pounds, hit nine home runs in each of the last two seasons at Brevard County and Wisconsin, but he wasn't trying to clear the wall in his last at-bat Sunday.
"Not really, cause every time I try to hit a home run, I end up rolling over or striking out," Gennett said. "So I was just trying to put a good at-bat together and try to hit the ball hard."
"He can hit," Brewers general manager Doug Melvin said. "Reid [Nichols, Milwaukee's farm director] said two years ago, 'This guy is going to hit in the big leagues.' He's always hit."
Brewers manager Ron Roenicke was managing Milwaukee's other split-squad game, at Maryvale Baseball Park against the Dodgers. He got word of Gennett's feat in the dugout.
"It would be nice to think he was 6-foot and 200 [pounds], but this guy keeps doing it," Roenicke said. "They're really high on him -- the Minor League [staff]."
Melvin mentioned other small-framed players who have made it in the Majors. That list is topped by Boston second baseman Dustin Pedroia, the 5-foot-9 2008 American League MVP, but also includes San Francisco utility man Mike Fontenot (5-foot-8) and Houston's Jose Altuve (5-foot-7).
Third baseman Taylor Green, the Brewers' Minor League Player of the Year in 2011, had three hits -- a single, double and triple.
Royals starter Felipe Paulino, bidding for a rotation role, gave up five runs on six hits in his 2 2/3 innings. Included were two triples and a double, and Paulino compounded his trouble by issuing three walks.
Gennett began the Brewers' three-run outburst in the first inning with a triple to right field. Paulino walked two batters and gave up one run on a wild pitch, another on his wild pickoff throw and a third on Green's triple to right.
In the second inning, Gennett followed singles by Edwin Maysonet and Nyjer Morgan with a run-scoring double. Paulino was pulled in the third after 78 pitches with two on and two outs. Reliever Tommy Hottovy was tagged for an RBI single by Maysonet.
Brewers starter Marco Estrada reeled off four shutout innings, giving up three hits, including a double by Mike Moustakas. He struck out four and walked one.
Lorenzo Cain, whose .488 average tied for the Major League lead going into the game, started a two-run Royals sixth against Josh Butler with a single and a stolen base. Eric Hosmer doubled and Billy Butler singled to drive in the runs. Minor Leaguer Terry Evans hit a solo home run in the eighth.
Royals right fielder Jeff Francoeur was ejected in the fourth inning by plate umpire John Tumpane after a disputed third-strike call.
Up next: Left-hander Chris Narveson starts in Goodyear, Ariz. on Monday against right-hander Justin Masterson and the Indians at 3:05 p.m. CT as the Brewers regroup after split-squad games Sunday and start to ramp up for the regular season. Expect the positional starters to begin playing more frequently and deeper into games, offering a better idea of what sort of offense the Brewers will field post Prince Fielder. Left fielder Ryan Braun will return to the lineup after taking Sunday off, and the Brewers hope shortstop Alex Gonzalez is able to start after missing Sunday with a bruised right heel.