The postseason is simple: Win enough games, you advance. Win enough series, and you're champs.
The final weekend of the regular season? Now that's where this beautiful sport truly gets wacky.
Sure, nine of the 10 playoff teams have already clinched -- with the Royals becoming the most recent to do so, snapping a 29-year postseason drought by virtue of their win over the White Sox on Friday night.
But the scenarios seem endless with two days remaining in a wild finish to this unpredictable season. Both Central divisions are separated by just one game and could be determined on the season's final day -- or later. And the Mariners are still very alive in their quest to catch Oakland for the last remaining playoff spot.
IF THE POSTSEASON STARTED TODAY ...
Wild Card: A's at Royals
Division Series: Wild Card at Angels | Tigers at Orioles
Wild Card: Giants at Pirates
Division Series: Wild Card at Nationals | Cardinals at Dodgers
• Postseason picture
Friday's action got off to a start in Washington, where the Nationals clinched home-field advantage throughout the NL playoffs for the second time in three years. They did so by virtue of an absolute gem from right-hander Doug Fister, who tossed a three-hit shutout against the Marlins on just 104 pitches.
Friday night's pennant-race action got started in Detroit with a bit of an unexpected twist in what's already been a wild AL Central race. The Twins put up three in the first and had built a six-run cushion on the first-place Tigers by the top of the fourth inning.
With their eventual 11-4 loss, the Tigers left the door open for the Royals, who took full advantage. Jeremy Guthrie tossed seven shutout frames, after the Royals jumped out to three runs in the first inning in Chicago against the White Sox.
By the time Michael Taylor's pop-up had settled into Salvador Perez's mitt for the final out, it was party time for the Royals. Not only had they moved within one game of the Tigers in the Central, but they had clinched their first playoff berth since 1985.
How long had it been? Of the Royals nine starters Friday night, only three were even born the last time Kansas City played a playoff game.
The A's kept pace with the Royals with a 6-2 victory of their own over Texas. That means the Royals' magic number for (at the very least) home-field advantage in the Wild Card Game is down to one.
But the A's weren't able to wrap up their own playoff spot Friday night. That's because the Mariners managed to stay two back with two to play by holding off the Angels. Despite the loss, the Halos clinched home-field advantage throughout the playoffs by virtue of Baltimore's loss earlier in the day.
Finally, the day of pennant-race action ended with some drama in the NL Central. The Pirates had knocked off the Reds earlier in the night, meaning a Cardinals loss to the D-backs would have moved the two clubs into a tie for first place.
But the Cardinals responded to some adversity. After blowing a three-run, eighth-inning lead, Jhonny Peralta singled home Daniel Descalso in the 10th, giving St. Louis a 7-6 victory, which cut its magic number to two.
TODAY'S KEY GAMES TO WATCH (all times ET)
Pirates (Liriano 7-10, 3.32) at Reds (Simon 15-10, 3.34), 1:05 p.m. Preview
Pittsburgh clinched home-field advantage in the Wild Card Game by virtue of the Giants' loss to the Padres on Friday night. But the Bucs' focus is on the Central as a red-hot Francisco Liriano (one earned run in his last 28 innings) takes the hill.
Twins (Nolasco 5-12, 5.47) at Tigers (Lobstein 1-1, 3.38), 7:08 p.m. Preview
The Tigers' Central Division cushion is down to just one, but if they can beat Minnesota, they'll be scoreboard watching. A win and a Royals loss would wrap up a fourth straight division crown for Detroit.
Royals (Duffy 9-11, 2.32) at White Sox (Danks 10-11, 4.82), 7:10 p.m. Preview
Danny Duffy has quietly become one of the most reliable left-handers in the American League, and he gets the start on the South Side. Duffy threw six shutout frames in his return from a shoulder ailment on Monday.
A's (Samardzija 7-12, 2.88) at Rangers (Holland 2-0, 1.31), 8:05 p.m. Preview
The A's fate is in their hands with two games to play. Win one game, and they'll clinch a Wild Card berth. Lose both games, and they risk dropping into a one-game playoff with the Mariners.
Cardinals (Lynn 15-10, 2.73) at D-backs (Miley 8-12, 4.35), 8:10 p.m. Preview
By the time the Cardinals take the field in Arizona on Saturday night, they'll know the result of the Pirates' game in Cincinnati. Should Pittsburgh lose, the Cardinals would be a win away from clinching back-to-back Central crowns.
Angels (Wilson 13-10, 4.61) at Mariners (Paxton 6-4, 3.03), 9:10 p.m. Preview
The Mariners' only path to the postseason is to win and get help. But if they can survive Saturday, they'll head into the season's final day just one game back with King Felix set to take the hill.
To calculate a team's magic number, take the number of games it has remaining and add one. Then subtract the difference in the number of losses between that team and its closest pursuer.
AL East: Orioles clinched
AL Central: Tigers 2 over Royals
AL West: Angels clinched
AL Wild Card 1: Royals 1 over A's
AL Wild Card 2: A's 1 over Mariners
NL East: Nationals clinched
NL Central: Cardinals 2 over Pirates
NL West: Dodgers clinched
NL Wild Card 1: Pirates clinched
NL Wild Card 2: Giants clinched
A tiebreaker game will be played to determine a division winner, even if the tied clubs are assured of participating in the postseason. If a division championship tiebreaker is necessary, the head-to-head record between the clubs will determine home-field advantage. If the head-to-head record is tied, then division record will be the next tiebreaker.
If two clubs are tied for the two Wild Card berths, home-field advantage will be determined by the head-to-head record between the clubs. If the head-to-head record is tied, then division record will be the next tiebreaker.
• Tiebreaker rules
AJ Cassavell is a reporter for MLB.com. Follow him on Twitter @ajcassavell.