As the season heads down the home stretch, five of the eight postseason races feature wide margins. In the American League Central (Indians), AL West (Rangers), National League East (Nationals), NL Central (Cubs) and NL West (Dodgers), the first-place team has greater than a 90-percent probability of winning the division.
But that still leaves three tight races that could change hands frequently over the final three-plus weeks of the regular season.
Here is a breakdown of those battles, looking at a key series for each, plus each relevant team's odds, remaining strength of schedule (SOS) and biggest question. Note that the SOS was calculated as the average winning percentage, through Thursday, of a team's upcoming opponents.
AL EAST
1. RED SOX: 78-61 (.561)
Probability of a division title: 56.3 percent
Remaining SOS: .528 (10 of 23 games at home). Boston only has division opponents left, and of its remaining games, all but three -- Sept. 23-25 at Tampa Bay -- are against clubs with winning records.
Biggest question: Boston's bullpen ranks 17th in the Majors with a 3.83 ERA, including 4.70 in August. Koji Uehara's recent return from the disabled list may help, but the unit could be tested in some big spots against the likes of Toronto and Baltimore.
2. BLUE JAYS: 77-62 (.554), 1 game behind
Probability of a division title: 32.5 percent
Remaining SOS: .510 (13 of 23 games at home). The Blue Jays still have to make a road trip to the West Coast, with four games against the Angels and three against the Mariners.
Biggest question: When the Yankees finished off a sweep of the Blue Jays on Wednesday in the Bronx, Toronto catcher Russell Martin left in the top of the ninth inning after tweaking his left knee. While he is considered day to day, the Blue Jays can't afford to lose Martin, who leads the club with a .931 OPS since the All-Star break.

3. ORIOLES: 76-63 (.547), 2 games behind
Probability of a division title: 9.8 percent
Remaining SOS: .511 (11 of 23 games at home). The Orioles still face road series at Detroit, Boston, Toronto and New York but do get a break by hosting Arizona for an Interleague set.
Biggest question: Baltimore ranks 26th in the Majors in ERA from the starting rotation (4.86) and 24th in innings. Chris Tillman is set to return on Sunday for his first outing since Aug. 20, and the O's will need him to produce like he has for much of the season.

Crucial series: Red Sox at Blue Jays, Friday-Sunday. A sweep either way would shift the balance of power significantly, as these teams clash for the first time since early June. They also will finish the season against each other, with three games at Fenway Park.
AL WILD CARD
1. RED SOX: 78-61 (.561), lead AL East
Probability of a Wild Card berth: 33.6 percent
2. BLUE JAYS: 77-62 (.554), 1-game lead for first Wild Card
Probability of a Wild Card berth: 48.0 percent
3. ORIOLES: 76-63 (.547), 1-game lead for second Wild Card
Probability of a Wild Card berth: 37.7 percent
4. TIGERS: 75-64 (.540), 1 game behind second Wild Card
Probability of a Wild Card berth: 43.7 percent
Remaining SOS: .480 (14 of 23 games at home). The Tigers have two series against the Indians, who have beaten them 11 of 12 times this season. On the other hand, they get two series with the Twins, whom they are 10-2 against.
Biggest question: Since Nick Castellanos sustained a broken bone in his left hand about a month ago, the Tigers have received little production from third base, including zero home runs. Castellanos might return with a couple of weeks to go in the season, but it's unclear what Detroit can expect from him down the stretch.
5. YANKEES: 74-65 (.532), 2 games behind second Wild Card
Probability of a Wild Card berth: 9.4 percent
Remaining SOS: .523 (12 of 23 games at home). After hosting the Rays this weekend, the Yankees welcome in the first-place Dodgers for an Interleague series, then must overcome a brutal road trip that features four games apiece at Boston and Toronto.
Biggest question: The Yankees are on an 18-9 roll, and their young guns have played a major part in that, including rookie Tyler Austin's walk-off homer to beat the Rays on Thursday. But it remains to be seen whether youngsters such as Gary Sánchez (6-for-35 with 12 strikeouts in his last nine games) can avoid fatigue and make the necessary adjustments.

6. ASTROS: 74-66 (.529), 2.5 games behind second Wild Card
Probability of a Wild Card berth: 15.9 percent
Remaining SOS: .509 (13 of 22 games at home). They will be tested by their upcoming homestand (four vs. Cubs, three vs. Rangers), but seven of their final 10 games are against the Angels, whom they have defeated 11 of 12 times this year.
Biggest question: Health is an issue right now for the Astros. Shortstop Carlos Correa (left shoulder inflammation) missed the past two games, and perhaps more concerning, it's unclear if and when pitchers Dallas Keuchel (left shoulder inflammation) and Lance McCullers Jr. (right elbow sprain) will return this season. That has left the team's rotation in a bind.
7. ROYALS: 72-67 (.518), 4 games behind second Wild Card
Probability of a Wild Card berth: 3.1 percent
Remaining SOS: .493 (14 of 23 games at home). The Royals, who are 42-25 at Kauffman Stadium, will host the sub-.500 A's, White Sox and Twins for a combined 10 games.
Biggest question: The Royals have been known for their bullpen the past few years, but during a 3-5 stretch, each of the team's losses has been charged to a reliever. Three of those belong to Joakim Soria, who has allowed 12 baserunners in 4 2/3 innings over that time while continuing to pitch in high-leverage situations.
8. MARINERS: 72-68 (.514), 4.5 games behind second Wild Card
Probability of a Wild Card berth: 5.0 percent
Remaining SOS: .469 (10 of 22 games at home). While Seattle is 32-37 away from Safeco Field and has to play a dozen more road games, nine of those come against non-contenders (A's, Angels, Twins).
Biggest question: A Mariners starting pitcher has allowed fewer than three runs just once in the team's past 18 games, and the club has four quality starts in that span. Can Félix Hernández (back-to-back six-run outings) lead the group to a better finish?
Crucial series: Orioles at Tigers, Friday-Sunday. Detroit has Michael Fulmer, Jordan Zimmermann (coming off the DL) and Justin Verlander lined up as it tries to jump over the Orioles and into playoff position.
NL WILD CARD
1. GIANTS: 74-65 (.532), 0.5-game lead for first Wild Card
Probability of a Wild Card berth: 70.0 percent
Remaining SOS: .482 (13 of 23 games at home). The Giants, who trail the Dodgers by five games in the NL West, still face their rivals six more times. The two teams meet at AT&T Park to end the season.
Biggest question: Since beating the Braves 13-4 on Aug. 28, the Giants have averaged fewer than three runs over nine games and posted a .544 OPS. Even Coors Field didn't cure the offense, which managed eight runs over three games there this week.
2. METS: 74-66 (.529), 0.5-game lead for second Wild Card
Probability of a Wild Card berth: 68.5 percent
Remaining SOS: .445 (10 of 22 games at home). The Mets only have three games left against teams currently above .500, playing at Washington to begin next week.
Biggest question: New York has won five straight and 14 of 18, but with Steven Matz on the disabled list and Jacob deGrom dealing with forearm inflammation, can rookies Robert Gsellman and Seth Lugo continue to hold the fort so effectively?

3. CARDINALS: 73-66 (.525), 0.5 games behind second Wild Card
Probability of a Wild Card berth: 48.3 percent
Remaining SOS: .517 (13 of 23 games at home). All the games at Busch Stadium might not be good news, considering St. Louis is a mystifying 30-38 there. A 10-game swing through San Francisco, Colorado and Chicago also looms.
Biggest question: How much impact can players returning from injury have? Michael Wacha and Trevor Rosenthal could be close to bolstering the bullpen, while rookie shortstop Aledmys Díaz (.894 OPS) might be back as early as this weekend.
4. PIRATES: 69-69 (.500), 4 games behind second Wild Card
Probability of a Wild Card berth: 5.7 percent
Remaining SOS: .497 (10 of 24 games at home). If the Bucs are going to make a run, now is a good time, as their next 14 games come against the Reds, Phillies and Brewers.
Biggest question: Since taking over at closer following the Mark Melancon trade, Tony Watson has blown three of 14 save opportunities while posting a 4.70 ERA.
5. MARLINS: 69-71 (.493), 5 games behind second Wild Card
Probability of a Wild Card berth: 1.3 percent
Remaining SOS: .494 (13 of 22 games at home). Miami still has a dozen games scheduled against the Dodgers, Mets and Nationals.
Biggest question:Giancarlo Stanton is back, having returned earlier than expected from a groin strain. But he is limited to pinch-hitting for now, so it's worth wondering just how much of a boost he can provide.
Crucial series: Cardinals at Giants, Sept. 15-18. St. Louis will kick off a 10-game road trip with a four-game set that could go a long way toward deciding the Wild Card race.