Kansas City, Mo. ? Big No. 5 has turned the big 5-0.

Twenty-seven years after he won his first batting championship and became known as “the kid at third base,” Hall of Famer George Brett’s happy, robust life reached a half century Thursday, which he spent — naturally — in front of a big crowd watching a sporting event.

Paired with pro Jerry McGee, Brett’s four-man team shot 16-under par during the pro-am prequel to this weekend’s Champions Tour event, the Bayer Advantage Celebrity Pro-Am.

A big 50th birthday bash was planned Thursday night. But Leslie Brett said her husband would prefer a quiet night with friends.

A large and appreciative galley followed Brett’s foursome. Ten years after retiring, he’s still the biggest sports celebrity in town, more popular than current stars Priest Holmes of the Chiefs or Mike Sweeney of the Royals.

In a memorable 21-year career, Brett collected 3,154 hits, three batting titles and an American League MVP award. His .390 average in 1980 remains the highest in any full season by any major leaguer since Ted Williams hit .406 in 1941.

“He’s aged remarkably well,” said Royals executive vice president Herk Robinson. “He’s got a beautiful wife, three great kids and he’s even strengthened his golf game. I have no doubt he could go out there and hit .250 right now.”

Robinson has known Brett since he was a scatterbrained teenager playing football and baseball and hanging out on Southern California’s beaches.

“In so many ways, he’s the same guy he was when he was 18. A great big heart, a great spirit and a twinkle in his eye,” he said.

Robinson still almost catches his breath when reminded that in 1971, the Royals passed on Brett in the first round of the June draft. If some other club had taken him before the Royals got around to calling his name in round two, the entire history of the franchise would have been different.

“One of the biggest mistakes we ever made,” Robinson said.

Over the objections of the scout who had found him, the Royals passed on Brett and took Roy Branch, a fire-balling left-hander from St. Louis who looked like Bob Gibson.

Brett, still there for the taking in the second round, soared to stardom. But arm trouble derailed Branch, who spent most of his career drifting through the minor leagues.

Brett turned out to be the central figure in the Royals’ glory years of 1976-85 when they won five division titles, two pennants and a World Series.

“We were so lucky,” Robinson said.