September began with major movement across the MLB playoff picture, with some of the biggest swings yet in RosterSpin's playoff model.
The biggest swings came in the American League, where several teams fighting over the final postseason spots moved sharply in opposite directions after Tuesday's results.
No team had a worse day in RosterSpin's model than the Houston Astros.
Houston's playoff probability fell 10.9 percentage points to 63.1%, while its chances of winning the AL West dropped 11.7 points to 59.9%.
The Astros' 5–1 loss to the Chicago White Sox helped tighten a division race that remains very much undecided.
Texas was one of the biggest beneficiaries.
Guardians and Rangers make major gains
The Rangers' 8–1 win over Oakland pushed their playoff probability up 8.9 percentage points to 40.0%.
Even more significantly, Texas' AL West probability jumped 9.3 points to 32.9%.
But the day's biggest winner may have been Cleveland.
The Guardians opened a crucial series against Toronto with a 6–1 victory and saw their playoff probability jump from 45.5% to 55.4% — a gain of 9.9 percentage points.
Cleveland's Wild Card probability climbed even more, increasing 10.1 points to 40.7%.
That result had an almost equal effect in the opposite direction for Toronto.
Blue Jays give back much of their weekend gain
Toronto entered the Cleveland series with considerable momentum after sweeping Seattle over the weekend.
RosterSpin's model had moved the Blue Jays' playoff probability from 15% to roughly 23% during that run.
One loss has already erased a significant portion of that gain.
Toronto's playoff probability fell another 6.7 percentage points Tuesday and now sits at 13.8%.
The Blue Jays are far from eliminated — their playoff elimination number remains 22 — but the first game of a head-to-head series against one of the teams they are chasing proved costly.
Baltimore also suffered a significant decline, with its playoff probability dropping 7.7 points to 18.7%.
The result leaves the middle of the American League playoff race extremely volatile as September begins.
White Sox strengthen their position
While several AL contenders moved dramatically, Chicago continued to strengthen its position.
The White Sox improved to 73–65 with their win in Houston.
RosterSpin now gives Chicago a 95.3% chance of reaching the postseason, up 2.8 percentage points from the previous snapshot.
Their AL Central probability also increased to 84.1%.
Just as importantly, Chicago's playoff magic number fell to 20.
That continues a notable progression for the White Sox. Their playoff magic number stood at 22 entering the Houston series, remained there following the opening loss, and has now fallen two steps following Tuesday's results.
MLB magic numbers will become increasingly important throughout September as teams move closer to clinching postseason berths. Chicago's playoff magic number is now 20, while several other contenders remain much further from securing their spots.
MLB playoff picture: biggest odds changes on September 1
The largest day-over-day playoff probability changes in RosterSpin's model were:
- Houston: 63.1% (-10.9)
- Cleveland: 55.4% (+9.9)
- Texas: 40.0% (+8.9)
- Baltimore: 18.7% (-7.7)
- Toronto: 13.8% (-6.7)
- Arizona: 38.3% (-3.6)
- Miami: 6.5% (+3.2)
- Chicago White Sox: 95.3% (+2.8)
With most teams having fewer than 25 games remaining, individual results are beginning to carry considerably more weight.
And nowhere is that more obvious than in the American League, where Houston, Cleveland, Texas, Baltimore and Toronto all saw their postseason probabilities move by more than six percentage points in a single day.
September has only just begun.