There have been 12 single-game tiebreakers in MLB history. Each of them brought the nerves and anticipation of a playoff matchup, even though they were played as regular-season games — but game No. 163 is now a thing of the past.

With an expanded playoff format launching this October, MLB decided there wasn’t enough room on the calendar to break ties in that extra-game manner anymore. Instead, a set of tiebreaking rules will now decide not only seeding but also who gets into the postseason altogether if 162 games aren’t enough to determine the 12-team field. This means that the series your favorite team played way back in the first half could have a huge impact on its playoff hopes.

“It’s going to become a big deal when everyone [the fans] wakes up and realizes what’s going on,” Milwaukee Brewers manager Craig Counsell said last month.

Counsell’s team could be impacted directly, as Milwaukee is currently on the outside of the last wild-card berth in the National League, chasing the San Diego Padres for that final postseason spot. But the Brewers will have to make up a little extra ground this year since they lost their season series to the Padres 4-3, meaning if the teams finish with the same record, San Diego is in and Milwaukee is out.

“We finished games against them in … early June,” Counsell said. “We were aware of it at the time, but there’s 110 games left at that point. There’s not much to be done.

“We knew the rule,” Counsell said. “Everyone knew it …They felt fitting a tiebreaker game into the schedule wasn’t feasible.”

The league understands some of the angst that could exist if a team is eliminated by a season series played around Memorial Day but says the trade-off of more teams in the mix for a playoff spot is worth it.

“We are excited that more of our fans will get to experience postseason baseball this year as part of the expanded playoff format,” Morgan Sword, executive vice president of baseball operations, said. “Due to the increased number of postseason games, we had to ensure that the regular season would end on time.”

Though the postseason format is spelled out in the recently signed collective bargaining agreement, there is discretion when it comes to the specifics of the tiebreaker rules that will allow the league to examine the impact and make changes if needed. As players and teams realize the stakes, the new rules could also lead to a further emphasis on head-to-head matchups.

“If they beat us, more than we beat them, it should go to them, so I’m totally fine with the rule,” St. Louis Cardinals manager Oliver Marmol said. “Our job is to not lose, so if someone did that better than us, then you go home.”

That will be highlighted more starting next year when each team will play only 13 games — down from 19 — within its own division. And the results in the first year of the new format already show the added importance of beating other teams with playoff hopes in head-to-head intraleague matchups.

“When we played the Padres, it was not like we put more of an emphasis on winning those games versus any other games,” Philadelphia Phillies president of baseball operations Dave Dombrowski said in an email. “However, after we won the series, we did discuss how big this series could become.”

The Phillies are just ahead of the Padres in the NL wild-card race, and though both teams might get in, their seed will be determined by the tiebreaker system if the two teams have the same record after 162.

Philadelphia won its season series against both San Diego (4-3) and Milwaukee (4-2), so it would win any tiebreakers between either of those NL teams. The Brewers now understand the task at hand: Beat the opponents above them by at least a game to take the tiebreaker out of it. Otherwise, it’ll be a heartbreaking end to their season.

“You are treating every game as an important game, but there’s a game the next day and the next day and the next day,” Counsell said. “You have to manage with both concepts in mind every day.”

What the new tiebreaker rules look like

With the new procedures already affecting this season’s homestretch, here are the five rules that govern tiebreakers:

Head-to-head record: Self-explanatory. And if more than two teams tie, then the team with the best combined winning percentage against the other teams wins the tiebreaker.

Intradivision record: If the head-to-head records are tied — this would happen only between wild-card teams that played an even number of games — then the best record within their own divisions determines the winner.

Interdivision record: If the first two tiebreakers don’t settle it, then the next one rates teams’ records within their own leagues but not including their own divisions.

Second-half intraleague games: If teams are still tied by this point, a winner will be determined by the winning percentage of each team within its own league over the final 81 games of the season.

Second-half intraleague games plus one (or more): If teams remain tied after the first four tiebreakers, then a winner will be determined by working backward from the final intraleague game of the first half until the tie is broken.

It should be noted, there are extreme scenarios, such as five-team ties, that the league doesn’t have an exact answer for. In these instances, there’s a clause that kicks in that would call for “commissioner’s discretion.” In other words, Rob Manfred might be choosing which team makes the postseason and which team doesn’t — though the scenario is far-fetched.

What does it all mean for this season’s races?

There are many close races this season, so there’s a chance that the tiebreakers could come into play. That being said, there is little to no chance of needing to use more than the first tiebreaker in any scenario this year. Either way, let’s take a look at how the new procedures impact some of the more exciting playoff and divisional races.

National League East: The New York Mets lead the season series over the Atlanta Braves 9-7. If the Braves sweep the final three games against New York, they’ll win the tiebreaker; otherwise, the Mets will come out on top. The winner will be the likely No. 2 seed and will get a bye. The loser will host a first-round playoff series.

NL Wild Card: As stated above, the Brewers lose a tiebreaker to both the Padres and the Phillies, while Philadelphia wins one over San Diego.

American League Central: It’s a three-team battle among the Cleveland Guardians, Chicago White Sox and Minnesota Twins, with the two losers likely left out of the postseason.

The White Sox currently lose tiebreakers to both teams, but they still have a chance to flip that script. They’ll need to sweep the Guardians this week in Chicago to win that season series, while they’re 6-7 against the Twins this season with six games left to play.

Cleveland has already won its season series with the Twins, so Minnesota would have to win one more game than the Guardians to beat them out for the division title.

AL Wild Card: This is where a tie has the best chance of occurring. The Seattle Mariners, Toronto Blue Jays and Tampa Bay Rays are neck and neck for all three wild-card spots. The two bottom teams of a tiebreaker won’t get a home game in the best-of-three first round.

The Mariners win a tiebreaker with the Blue Jays but lose one against the Rays. Meanwhile, Tampa Bay leads the season series with Toronto 8-7 with four games remaining between the teams.

The new system — and the elimination of game No. 163 — is bound to create some headlines if head-to-head records bounce someone from the playoffs or deliver a bye to a division winner. This year still has all the possibilities.