On July 7, 1922, Rogers Hornsby capped off a Cardinals comeback with a ninth inning walk off shot that propelled the Birds to a 6-5 victory over the visiting Brooklyn Dodgers at Sportsman's Park. Hornsby's big blast was his 21st of the season, which matched his total of the previous season. The 26-year-old who became known as "Rajah" was on a record breaking tear as he chased both the modern day National League record, as well as the League's all time record. The modern day record (post 1900) of 24 had stood since 1915 and was owned by Gavvy Cravath of the Phillies. Hornsby's 25th came on July 19th with another walkoff in St. Louis, and the National League's all time record which was held by Chicago's Ned Williamson was broken on August 5th. Unfortunately the 27th blast came during a 2-1 loss, but it did not stop the home run swinging bat of Hornsby who would end up shattering the record with 42 homers on the season.
The record stood until Chuck Klein of the Phillies blasted 43 in 1929. It was a short lived run as the National League's single season home run king, but it was still a season to be remembered as he topped the .400 mark for the first time as he worked on his Hall of Fame resume.
Check out the box score here: http://www.baseball-reference.com/boxes/SLN/SLN192207070.shtml