Cleveland Indians pitchers Phil Niekro and Steve Carlton combine to beat the Toronto Blue Jays, 14 – 3, making it the first time in major league history that two 300-game winners pitch for the same team in the same game. Niekro goes six innings to get his 312th career win and Carlton blanks Toronto for three innings.

On April 8, 1987 – Cleveland Indians pitchers Phil Niekro and Steve Carlton combine to beat the Toronto Blue Jays, 14 – 3, making it the first time in major league history that two 300-game winners pitch for the same team in the same game. Niekro goes six innings to get his 312th career win and Carlton blanks Toronto for three innings.

Source
Baseball Reference April 8