The following year, 1906, Cobb became the Tigers' full-time center fielder and hit .316 in 98 games, setting a record for the highest batting average (minimum 310 plate appearances) for a 19-year-old (later bested by Mel Ott's .322 average in 124 games for the 1928 New York Giants). He never hit below that mark again. After being moved to right field, he led the Tigers to three consecutive American League pennants in 1907, 1908 and 1909. Detroit would lose each World Series (to the Cubs twice and then the Pirates); however, with Cobb's postseason numbers far below his career standard. Cobb did not get another opportunity to play on a pennant-winning team.
In 1907, Cobb reached first and then stole second, third and home. He accomplished the feat four times during his career, still an MLB record as of 2020. He finished the 1907 season with a league-leading .350 batting average, 212 hits, 49 steals and 119 runs batted in (RBI). At age 20, he was the youngest player to win a batting championship and held this record until 1955, when fellow Detroit Tiger Al Kaline won the batting title while twelve days younger than Cobb had been. Reflecting on his career in 1930, two years after retiring, he told Grantland Rice, "The biggest thrill I ever got came in a game against the Athletics in 1907 [on September 30]... The Athletics had us beaten, with Rube Waddell pitching. They were two runs ahead in the 9th inning, when I happened to hit a home run that tied the score. This game went 17 innings to a tie, and a few days later, we clinched our first pennant. You can understand what it meant for a 20-year-old country boy to hit a home run off the great Rube, in a pennant-winning game with two outs in the ninth."
In September 1907, Cobb began a relationship with The Coca-Cola Company that lasted the remainder of his life. By the time he died, he held over 20,000 shares of stock and owned bottling plants in Santa Maria, California, Twin Falls, Idaho, and Bend, Oregon. He was also a celebrity spokesman for the product. In the offseason between 1907 and 1908, Cobb negotiated with Clemson Agricultural College of South Carolina, offering to coach baseball there "for $250 a month, provided that he did not sign with Detroit that season". This did not come to pass, however.