Sandy Koufax surpassed Christy Mathewson's National League single-season strikeout record on September 27, 1961, striking out seven batters over eight innings in a 2-1 loss to the Philadelphia Phillies. Koufax finished the 1961 season with 269 strikeouts, a then-MLB record.
From the collection: Sandy Koufax fan-cave plaque →
Source: Historical record