The buyer paid $1.2 million for the 1909 card in an online auction that ended early Friday.
Bill Goodwin, a Missouri collectibles dealer who ran the auction, says he's thrilled with the final price.
The St. Louis Post-Dispatch reports the buyer went to bed after winning the 14-bid auction shortly after 2 a.m. Friday. Goodwin says the buyer hasn't decided if he wants to be identified.
The card was owned by a Houston businessman who didn't want to be identified.
Only about 200 of the cards were made and only about 60 are believed to still exist.
Wagner, a shortstop, was in the first class ever elected to the baseball Hall of Fame.
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