Brock concluded his career with 3,023 hits and dazzled fans with his basestealing exploits. In 1974, he broke Maury Wills' single-season steals record and finished the year with 118. In 1977, he eclipsed Ty Cobb's career-record 892 steals and went on to rack up 938 before retiring in 1979. There were two World Series titles with the Cardinals in 1964 and 1967 and a near-miss in 1968 when St. Louis couldn't close out the Tigers in the World Series after building a 3-1 series lead.
All along that happy road to Cooperstown, Brock maintained a close relationship with O'Neil.
"With Buck, it was almost a father-son relationship," Brock said recently while attending Fanfest activities in conjunction with the 2012 All-Star Game. "I met Buck when I was 19 years old. He looked at me and thought I had some talent."
O'Neil went on to become a Cubs' coach in 1962, just as Brock was arriving on the Major League scene after a short stint in the Minors.
"Buck's first year in the big leagues, I was his roommate," Brock said. "We kidded a great deal about having someone who was like your father right there with you. Buck was a good baseball man. He knew the game."
Brock struggled to solve big league pitching while with the Cubs, and Chicago wound up trading him to the Cardinals early in the 1964 season. The headliner coming Chicago's way was right-hander Ernie Broglio, who had won 18 games the previous season.
Historians note that when the deal was consummated, the prevailing opinion was that the Cubs had pulled off a heist. But it was actually St. Louis pulling off the heist as Brock flourished with the Cards and Broglio fizzled with the Cubs.
"Every year, this trade is ranked one of the worst [from the Cubs' standpoint] in the history of baseball," Brock said. "But at the time, I was in my third year in the big leagues and really struggling. To that point, I had never hit above .260 in the Majors. In the Minor Leagues and in college ball, I never hit below .350. At .260, you feel you don't really belong.
"I got a call from the general manager and he said my contract was being transferred to the Cardinals. My question to him was: 'What do they want with me?'"
Brock made an immediate impact in taking over the Cards' left-field job a year after the retirement of Stan Musial. St. Louis pulled off an amazing late-season comeback to win the National League pennant and then took down the Yankees in the World Series.
Brock had not only world-class speed and great base running instincts, but a passion for studying pitchers' moves and knowing how to get a jump.
"You can't run fast unless your shoulders are square to where you are going," Brock said. "You have to snap your body around so that it is squared up in one motion. And then you have to work on the lead. A normal base runner takes a 3 1/2 step lead. But a true base stealer wants 4 1/2 steps while making it appear that he's only going out 3 1/2 steps."
Brock was also a student of hitting. To pick up the spin on a pitcher's delivery, he knew in an instant that a glow represented a fastball and a dot moving either way meant it was a breaking ball.
"I got it right about 3,000 times," Brock said with a smile.
Brock, 73, has prospered as a businessman since his retirement and is an ordained minister. He's also a special instructor for the Cardinals and prominent whenever St. Louis legends gather for big events at Busch Stadium.
O'Neil knew Hall of Fame ability when he saw it. When he discovered Brock, he truly found a rare gem.
Robert Falkoff is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.