April 20

From The Met Wiki

1967: Tom Seaver wins his first game in the majors as the Mets defeat the Cubs, 6-1. Seaver pitches seven and one-third innings and records five strikeouts.

2000: Melvin Mora hits a home run in the tenth inning to give the Mets a 5-4 win over the Brewers at Shea Stadium. It is Mora's first home run ever in a regular season major league game.