So much for all those races being decided early. If the past month has proven anything about baseball, it's that you never really know what's going to happen, no matter how dominant or how mortal a team looks.
With that as a backdrop, we present the races for postseason home-field advantage, which were long considered foregone conclusions in both leagues and are now suddenly back in play.
The Astros rode an amazing start to a lead for the American League's best record that looked insurmountable for months. The Dodgers rolled past so much of the National League, so historically and for so long, that even the possibility of them not enjoying a majority of the postseason from Dodger Stadium seemed absurd.
• MLB standings
Yet here we are. Had its start not been so historic, Los Angeles would be in panic mode right now, with the wheels of their juggernaut suddenly sputtering off. And the Indians have done the seemingly impossible -- won 18 straight to surpass the Astros as the AL's best team.

Suddenly, the postseason picture, even for the teams who know they'll be playing in it, doesn't seem set in stone.
Let's take a look at the sudden drama that's been injected into both races and where they stand with three weeks left to play.
(But first, a quick refresher on tiebreaker rules: Home-field advantage is determined first by head-to-head records, then by higher winning percentage in intraleague games. If a further tiebreaker is needed, it's the best winning percentage in the last half of intraleague games.)
Now to the races.
NL
A month ago, nobody in their right mind would've predicted that home-field advantage in the NL would still be up for grabs. But the Dodgers have lost 10 straight for the first time in 25 years, and 15 of their past 16 games overall. Los Angeles' 2017 regular season no longer has the chance to be historic for the right reasons.
Even despite their recent struggles, the Dodgers still shouldn't have trouble wrapping up the NL West at some point. They still lead the D-backs by nine games, a number that speaks to just how dominant they were prior to this stretch. But their lead over Washington for home-field advantage has shrunk from 14 1/2 games to four games in just 2 1/2 weeks.

The Nationals, who clinched the NL East title on Sunday, now have a very real shot at earning home-field throughout the NL playoffs. The three-game set between the clubs in Washington this weekend will go a long way toward deciding both the league's best record as well as the potential tiebreaker between the two teams (Washington currently leads the season series, 2-1).
AL
The Astros appeared to have home-field advantage locked up for four months, as Houston held the AL's best record from May 10 until, well, this weekend. The streaking Indians finally surpassed them with Sunday's 3-2 win over the Orioles.
Cleveland has made up 7 1/2-game deficit to Houston during the streak, which is amazing because the Astros haven't played poorly: Houston is 9-8 during the stretch, and which included a seven-game win streak.

Yet the Astros entered Monday's off-day a game behind the Indians, who, of course, had home-field advantage last postseason and lost Game 7 of the World Series at Progressive Field. Boston, at 81-62, sits six back of Cleveland and five behind Houston.
The Indians own the tiebreaker over the Astros, but the Red Sox own the tiebreakers against both Cleveland and Houston at this point. The Red Sox and Astros still have another series against one another.
World Series
The 2017 World Series will be the first since MLB stopped using the winner of the All-Star Game to determine home-field advantage for the Fall Classic, which means Game 1 and Game 7 will be hosted by the pennant winner with the better regular-season record. Though it didn't end up helping Cleveland last season, this is the ideal situation for every playoff team.
It's determined in a simple way: Who had baseball's best record during the regular season?
Right now, that's still the Dodgers (92-51), who own a four-game advantage over the Nationals (88-55). The Indians sit one game behind Washington at 87-56, and the Astros (86-57) are one game behind the Indians.
At this time of year, a few extra wins here and there can make a huge difference a month from now, when the weather turns cool and everything is on the line.