The old axiom in baseball states that it’s the successes over the long haul that determines the best teams—not the short sprints. But when fall arrives, those that can carry momentum through short series and get hot at the right time often prevail.

Two division races remain in doubt, while the locations of both Wild Card match-ups have yet to be determined. So, as we reach the regular season’s final weekend, there is still plenty to be decided and several series to keep an eye on.

Angels vs. Mariners
It’s unfortunate that the lasting impression we may have about the Mariners is that they faltered severely near the finish line—especially the starting pitching. That’s because Lloyd McClendon and Seattle most certainly overachieved in 2014.

Even with the addition of high-priced free agent Robinson Cano, the M’s weren’t expected to be more than a club that—at its best—could get to .500. Instead, they have 84 wins (after beating Toronto on Thursday) with one three-game set remaining against the Angels, who are still trying to secure the AL’s best record and home-field throughout the postseason. They’ll need 86 or 87 (with plenty of help) in order to keep their waning postseason flame burning.

A’s vs. Rangers
There are many responsible for the A’s recent freefall, which saw the club go from AL pennant favorites to AL Wild Card hopeful in the span of a couple months. But to pinpoint the current area of weakness, it’s most certainly the offense.

The A’s are collectively hitting a paltry .220 for September. That offensive futility continued on Thursday in Arlington against the Texas Rangers, as Oakland only produced one run and ultimately lost the first of this four-game set on an Adrian Beltre walk-off homer. Entering play on Friday, Bob Melvin’s club now holds the second AL Wild Card spot, one game behind Kansas City and two games ahead of desperate Seattle.

Those on the Rangers that have been with the club for at least the past couple of years must be thinking about the possibility of sweet revenge from 2012—when the A’s rallied late overtake Texas for the division crown on the regular season’s final day. The Rangers’ slide that year ended with a loss in the AL Wild Card game.

Royals vs. White Sox
In a society riddled with exaggerations and overblown statements, this one is not: the Kansas City Royals are embarking on the franchise’s most important games in three decades. Barring a major collapse, Kansas City will see postseason baseball for the first time since its World Series-winning year of 1985.

A late rally—which included an Eric Hosmer home run and four hits from Lorenzo Cain—reduced the Royals’ playoff magic number to one in a 6-3 road win Thursday against the White Sox. By taking care of business themselves and maintaining its success against Chicago this year (12-5 in the season series), K.C. will be celebrating soon. With a bit of help from the Twins, they Royals may be able to make up a two-game deficit to the Tigers and recapture the AL Central.

Twins vs. Tigers
Turn back the calendar two months, and nobody—even the Tigers themselves—thought they would have to sweat it out to the last weekend to determine their playoff fate. But after a rough August, Detroit has righted itself in September to regain a slight AL Central lead on determined Kansas City.

The Tigers have showed their muscle of late with Victor Martinez hitting nearly .400 this month and is in the hunt for the batting title, while two-time MVP Miguel Cabrera has drilled seven September homers. Both contributed last night with round-trippers, and closer Joe Nathan had a rare uneventful ninth to finish off a 4-2 win over his former Twins at Comerica Park.

While Nathan closed it, Max Scherzer started it and notched his 18th victory. Neither he, nor Justin Verlander will get the chance to start and cement a playoff berth. Instead, Brad Ausmus’ rotation this weekend has an unknown (Kyle Lobstein) squeezed in between two capable veterans (Rick Porcello and David Price).

Cardinals vs. Diamondbacks
The entire NL playoff field has been decided. Who, where and when they play remains an unknown. St. Louis appeared to have the Central locked up once they passed Milwaukee with a spurt of nine wins in a 10-game span in early September.

Now, it’s the Pirates who are the division’s hot club and have closed in to within one game of the Cards. If Mike Matheny’s team can hold serve, the Bucs’ run will be futile. However, a letdown against the lowly Diamondbacks could mean the unenviable position of a Wild Card game. Having 15-game winner Lance Lynn taking the hill on Saturday with 20-game winning Adam Wainwright going on Sunday can easily erase any doubts and place St. Louis in the Division Series.

Pirates vs. Reds
After 21 straight years of futility, the Pittsburgh Pirates are stringing together a much more appeasing streak. Tuesday night’s win over Atlanta clinched a second consecutive playoff appearance for the franchise. It also continued to Bucs’ recent hot streak—currently with 16 wins over the past 20 games.

This sizzling September has been sparked by several contributors. Catcher Russell Martin leads the club with 16 RBIs this month, while the now-healthy Andrew McCutchen makes his claim for a second straight MVP with five home runs 1.063 OPS. Josh Harrison has been the steadiest member of the lineup—currently riding a 13-game hitting streak and posting 32 hits since the turn of the calendar.

Momentum is sometimes seen as an overrated factor in baseball, but there’s no denying that Pirates are the team that no one wants to face right now.