ESPN is airing a new documentary called "Long Gone Summer" on Sunday night. It will look back at Mark McGwire and Sammy Sosa's legendary 1998 chase to break Roger Maris' 61-homer season -- a record set in 1961, coincidentally. Heading into 1998, McGwire and Ken Griffey Jr., in that order, were the subjects the baseball world followed in hopes that one or both would hit at least 62 homers. 

It made sense. McGwire hit 58 homers between two teams in 1997 while Junior clubbed 56 for the Mariners. Next was Larry Walker with 49. Sosa, meanwhile, was not among the group of 12 players to hit at least 40 in 1997.

But then, Sosa had one of the craziest and homer-happy months in baseball history in June 1998.

Sosa was a slugger heading into the year. He was not an upper-tier slugger, though. He hit 36 homers in the 144-game 1995 season. He hit 40 in just 124 games in 1996 and then 36 in 1997. He didn't get off to a roaring start in 1998, either. He only homered three times in the first 20 games of the season. Through May 24, he hit nine homers in 49 games. For comparison's sake, McGwire had 24 through 45 games on that same date. 

As such, the scoreboard through May 24 wasn't much of a contest: 

  1. McGwire: 24
  2. Sosa: 9

Sosa's surge actually started right before June. On May 25 he hit two. On May 27, he hit two more. 

Heading to June, though, it was still a blowout:

  1. McGwire: 27
  2. Sosa: 13

On June 1, Sosa hit two more homers and the biggest home run month in MLB history was underway. Starting June 3, Sosa homered in five straight games. He went three without a long ball, but then hit one on June 13. 

A look at the June 15 scoreboard:

  1. McGwire: 31
  2. Sosa: 21

And then the floodgates truly flew open for Sosa. On June 15 against the Brewers at Wrigley Field, Sosa clubbed three homers. 

(A 20-year-old Matt Snyder may or may not have been ejected from the park for throwing his hat on the field after the third, but that's neither here nor there.)

All of a sudden, the (much closer) scoreboard looked like this:

  1. McGwire: 31
  2. Sosa: 24

"Slammin' Sammy" wasn't done by any stretch. 

He homered on June 17 and then on June 19-20 he hit two homers each game. He followed on June 21 by "only" hitting one. 

Through June 21: 

  1. McGwire: 33
  2. Sosa: 30

At that point, Sosa had clubbed 21 home runs in a 22-game span, one of the most prolific stretches in baseball history to this day. 

The rest of the month, McGwire hit four to Sosa's three. So we headed to July with the scoreboard: 

  1. McGwire: 37
  2. Sosa: 33

Remember, McGwire had a 15-homer lead on May 24 and a 14-homer lead heading to June. 

Sosa ended up with a 20-homer June, which isn't just a record for that month. It's the record for home runs in any month in the history of baseball. Here are the nine instances where a player hit at least 17 home runs in a month in history. 

Player

Month, Year

Home runs

Sammy Sosa

June, 1998

20

Giancarlo Stanton

Aug., 2017

18

Rudy York

Aug., 1937

18

Babe Ruth

Sept., 1927

17

Rudy York

Aug., 1943

17

Albert Belle

Sept., 1995

17

Willie Mays

Aug., 1965

17

Sammy Sosa

Aug., 2001

17

Barry Bonds

May., 2001

17

NOTE: "Sept." months also statistically include any regular season games played in October. Thanks to baseball-reference.com's excellent stathead for the sorting)

We know how the rest of the story unfolded, but Sosa's June run is what made this thing a two-horse race among division rivals. Without that, who knows how McGwire holds up under the pressure. The animated Sosa seemed to loosen McGwire up and help him to enjoy the chase. McGwire often seemed annoyed at all the attention for much of the season until the last few months, when Sosa became a veritable partner in the chase. It made it all the more fun that they played for the Cardinals and Cubs. 

That all started May 24, unbeknownst at the time to the baseball world, and carried through an incredible June 22 years ago.