On September 20, 1928, in an 8-5 win over the Giants at the Polo Grounds in New York, outfielder George Harper became the first man in the history of the Cardinals organization to hit three home runs in one game. Harper accomplished the feat in the first game of a doubleheader that had pennant implications on the line as the Giants came into the day trailing the Cardinals by just two games as both teams were fighting for the National League crown. Harper began his history making day with a solo shot off of Rube Benton in the second that put the Cardinals on the board first. He continued his assault on the baseball with a three run shot off of Benton in the sixth that opened up a 5-0 lead. The Giants did most of their damage with home runs off the bats of catcher Shanty Hogan and second baseman Bill Terry and by the time the top of the eighth rolled around the Cards were clinging to a narrow 6-5 lead, then Harper hit his third long ball of the day. This time it was a two-run shot off of Jack Scott that gave the Redbirds a little breathing room. The Cardinals starter Bill Sherdel pitched two scoreless innings to cap off the victory while locking down his 19th win of the season. The Giants took the second game by the score of 7-4, but the day ended just like it started with the Cardinals two games in front for the lead in the National League. Nine days later they would clinch the National League Pennant as they held on to the two game edge on their way to a World Series appearance. The home runs by Harper were the 15th, 16th, and 17th for him in a Redbird uniform and the last three of that season for the 36 year old well traveled outfielder. He spent just one season with the Birds, in that one year he made history with three swings of the bat as he sent the ball over the wall in New York.
Check put the box score: http://www.baseball-reference.com/boxes/NY1/NY1192809201.shtml
You can check out Harper's career numbers here: http://www.baseball-reference.com/players/h/harpege02.shtml