One day before Harmon Killebrew joined the 500-home run club, he spent his off day trying to outslug Willie Mays, already a member of the 600-home run club, in a midseason exhibition at Metropolitan Stadium on Aug. 9, 1971.The entire spectacle feels like a relic of another era, when two teams could spend an off day playing a game that would be almost unfathomable in today's MLB.Before first pitch, Killebrew and Mays held their own three-round home run contest, allowing Minnesota fans to watch two of baseball's premier power hitters swing for the fences. Former Twins and Giants pitcher Paul Giel served as the pitcher.There was enough interest that the crowd of 24,719 delayed the contest by approximately 20 minutes while fans found their seats. Only three Twins home dates drew more people during the entire 1971 season.An Exhibition Worth Remembering Former Giants great Willie Mays is photographed at the team's new home, Pacific Bell Park, in downtown San Francisco. | USA TODAY Network via Reuters ConnectMays ultimately won the showdown 6-4, beating Killebrew for the second time in a home run contest. The two had previously faced each other on the televised Home Run Derby program filmed before the 1960 season, with Mays winning that meeting 7-6.Minnesota was hardly unfamiliar territory for Mays, though. Twenty years earlier, a 20-year-old Mays played 35 games for the Triple-A Minneapolis Millers, batting .477/.524/.799 with eight home runs before earning his promotion to the New York Giants. Back in Minnesota two decades later, the Say Hey Kid made sure to put on a show.Mays started the game in center field before moving around the diamond, appearing at first base, second base, shortstop and third base before departing in the sixth inning. Though best remembered for his dazzling work in center field, he had already made occasional Major League appearances at first base, shortstop and third base in addition to playing all three outfield spots. His tour around the infield, including a rare turn at second, added another wrinkle to an already unusual exhibition.Killebrew got in on the positional experimentation as well, although his best work came with a bat in his hands.He entered the exhibition stuck on 499 career home runs, a number he had been sitting on since July 25. Killebrew then launched a three-run homer in the first inning of Minnesota's 5-2 win, only for the blast to remain unofficial because the game did not count in the standings.Fans hoping to witness history did not have to wait much longer. Facing the Baltimore Orioles on Aug. 10, Killebrew hit No. 500 off Mike Cuellar in the first inning before adding No. 501 later in the game. He had now trotted around the bases three times in just over a day, but only two of those trips made it into the official record book.Those circumstances make Aug. 9 feel like more than a meaningless detour in a long 162 game season. The game set the stage for one of the biggest milestones of Killebrew's career the following night while giving nearly 25,000 fans a rare chance to watch two all-time greats turn an off day into something truly memorable.Add us as a preferred source on GoogleFollow