You cannot get this by simming any of the World Series games. You may sim all games up to the World Series, but you must play all of the World Series games or the achievement will not pop. The game can be very unforgiving with simming, so it might take a few attempts of simming through the season and the first couple rounds of the playoffs. The team I found to be most consistent with making the playoffs and getting wins by simming in the playoffs was the Dodgers, but it's pretty unpredictable so you can do it with just about any good team.
When I got the achievement, I chose the Dodgers, full 25 man roster, 52 game season. I simmed the playoffs all the way to 3-3 in the NLCS and played the last game and all of the World Series games and the achievement popped.
For those needing more detail or those less familiar with baseball and how the playoffs work, from the main season screen, go up to the schedule at the top of the screen and press
. Use
to advance to June and press
again on any day after the last game. Confirm the warning (it will not affect this achievement but will affect others like the season stats achievements). Then press
to Advance to the Playoffs.
Assuming you made the playoffs, you will be on the Postseason screen. If you didn't make the playoffs, you can advance to the next season and sim to the end again and hope for a better record. I've gotten anywhere from a 32-20 record to a 21-31 record with the same team so it may take a few tries to make the playoffs.
Once at the Postseason screen, sim one game at a time by pressing
. The Wild Card game is a single game series so if you lose that game you will have to start the process over, but hopefully your team did well enough that you skipped the Wild Card round and are in the NLDS/ALDS. The DS round is a best of 5 series so 3 losses and you're out. The CS round is a best of 7 series so 4 losses and you're out. It's up to you whether you want to risk simming all of the games and possibly having to start over, or stopping once you reach 2 losses in the DS and 3 losses in the CS and just playing the rest of the games in each series to make sure you advance. Unfortunately you cannot turn autosave off, so it can be a tedious process to get to the World Series and depending on your luck with simming you may end up having to play quite a few games in the first couple rounds of the playoffs to make it to the World Series.
Once you win the NLCS or ALCS and are in the World Series, simply play the rest of the games (no simming). Once you have won 4 games in the World Series, the achievement will pop immediately at the end of the game. Don't forget to set the CPU Difficulty to Easy from Settings on main menu to make it as easy as possible to win the games. I also recommend setting the Fielding Controls to Assisted and Ball Height Indicator to Static, as the fielding can be quite difficult on the default settings.