It's been nearly two decades since Fernando Tatis hit two grand slams in one inning

For most Major Leaguers, just hitting one grand slam is a career highlight. Derek Jeter needed nearly a decade -- 6,542 at-bats! -- to hit his first, and he's done seemingly everything a baseball player can do. 
So you'd think that, once the stars have aligned and you've hit that grand slam, you wouldn't get greedy. You just drove in four runs with one swing, after all, and it's not like you're likely to do it again in the same game: Only 13 players have pulled that off, and none since Josh Willingham back in 2009. 
Of course, former Cardinals third baseman Fernando Tatis didn't concern himself with hitting two in one game. On April 23, 1999, at Dodger Stadium, he hit two in the same inning: 

Tatis was a solid player over 11 Major League seasons, and 1999 turned out to be the best year of his career: 34 homers with a .298/.404/.553 slash line. He was so good that he very nearly convinced St. Louis to trade away its promising third-base prospect, some guy named Albert Pujols .
Still, he'll always be remembered for those two swings at Chavez Ravine. Even Vin Scully, the man who saw everything from World Series walk-offs to Hank Aaron's 715th homer, was left speechless.
"When he came up the second time, I said, 'I'm not even going to look in the record book because I can't believe anybody could have ever [hit two slams in an inning],'" Scully told the St. Louis Post-Dispatch. "And then damned if he didn't do it. What would it be comparable to? I don't know how you could compare it to anything. One inning is so preposterous."

But that's not the only home run preposterousness to take place on April 23! Also on this date in baseball history: Justin Upton and Melvin Upton Jr. -- in their first season as Major League teammates, and only the second time they'd hit consecutively -- went back-to-back for the Braves against the Rockies.

Somewhat amazingly, that wasn't even the first time two brothers had pulled off the feat: Lloyd and Paul Waner, who spent 14 years together with the Pirates, hit back-to-back homers against the Giants on Sept. 15, 1938.