Since 1996, the first full season with at least one wild card, 104 of 132 division champions (79 percent) held at least a share of the division lead entering September.
Last year, all six of the division leaders entering September went on to win their divisions: the Red Sox, Indians, Astros, Washington Nationals, Cubs and Los Angeles Dodgers. It was the fourth time that had happened since 1996. The other times were in 1999, 2001 and 2002.
Since 1996, there has not been a season in which none of the division leaders entering September went on to win their divisions.
With the Red Sox (7½) and Indians (14) each leading their divisions by large margins. it's worth noting that the largest division lead entering September for a team that did not end up winning that division is 7½ games by the 1995 Angels, who missed out on the playoffs entirely when the Yankees won that year's wild card.
Since 1996, four teams have had a division lead during September (through games of a given date) of five or more games and failed to win the division: the 2009 Tigers (7-game lead), 2007 Mets (7), 2006 Tigers (5½) and 2012 Rangers (5½) (Source: Elias).
The Indians are up 14 games in the AL Central. But what does that lead get you? Since 1996, only two of 16 teams to lead their division by 14 or more games entering September have gone on to win the World Series.
What about the wild cards?
In the multiple wild-card era (since 2012), there has been only one season when each team in wild-card position on Sept. 1 held on to make the playoffs -- and it was last year, when the Yankees, Twins, Diamondbacks and Rockies did so.
Also of note, the Red Sox and Yankees each have winning percentages of .630 or higher.
According to Elias, the last time at least two teams in the same league had winning percentages of .630 or higher entering September was in 1998, when the Braves (.652), Padres (.645) and Astros (.630) did so in the NL.
Also from Elias, this is the first time in the divisional era (since 1969) that two or more teams in the same division have had winning percentages of .630 or above entering September.
Meanwhile, the Royals and Orioles both have winning percentages below .325.
According to Elias, the last time two teams in the same league entered September with winning percentages under .325 was in 1979, when the Blue Jays (.321) and A's (.324) did so.