A native of Menasha Wisconsin, Dave Koslo joined New York Giants in 1941 at age 21 pitched two seasons and then proudly served three years, 1943-1945 in the US Military during World War II
In 1949 Dave Koslo was the veteran of manager Leo Durocher's New York Giants pitching staff during the late 1940s. The southpaw had pin-point control and led the entire NL in ERA with 2.50 in 1949... issued just 43 walks in 212 innings of work and completed 15 games... in 1949 Koslo posted a 11-14 record for a team that ended 24 games out of first place. A well-noted mound workhorse Dave Koslo posted at least 10 wins six seasons, and worked seven straight years of over 149 innings, including 3 years of 200 innings, with a high of 265.1 in 1946 when he led the National League in games started. Dave Koslo completed an astonishing 74 of 189 career games started. .