Cinergy Field, formerly Riverfront Stadium, was the only current US Major League stadium in which McGwire had played a regular-season game without hitting a home run - until Thursday's effort. McGwire's home run was his 33rd of the year and 490th of his career, and came with one out in the ninth.
In Montreal, Orel Hershiser became the 95th pitcher to win 200 games and the third among active pitchers, behind Roger Clemens and Greg Maddux, as he helped the New York Mets overcome the Expos 7-4.
Elsewhere, Bernie Williams hit a two-run homer, leading the New York Yankees to a 5-4 victory over Tampa Bay in their 15,000th game since entering the American League.
In Cleveland, a mix-up by the Cleveland manager, Mike Hargrove, helped the Toronto Blue Jays to a 4-3 victory over the Indians. The mistake meant Charles Nagy became the first pitcher to bat in an American League park since Jim Kern on July 28, 1978. Hargrove originally listed Manny Ramirez as a designated hitter and named namesake Alex Ramirez in right field. But after Toronto's first innings, Manny Ramirez took his usual place in right field.
The case of mistaken identity on the team card meant that the Indians had to forfeit their designated hitter.