May 20
1999 — Robin Ventura becomes the first major leaguer to hit grand slams in both games of a doubleheader, leading the New York Mets to a sweep over Milwaukee, 11-10 and 10-1.
2001 — Barry Bonds hits two homers in San Francisco's 11-6 loss to the Atlanta Braves for a total of five in two games, making him the 23rd player in history to do so.