Pct = .5 + 1.3246*OPSDIFF
The tables below show what the Royals hit and allowed this year. Their big advantages are with RISP and when it is Late & Close. They had differentials of .052 and .057 in those two cases.
|Late & Close||0.245||0.310||0.340||0.650|
|Late & Close||0.221||0.292||0.300||0.593|
If I use some research I did a few years ago, Does Team Clutch Matter in Baseball?, where I estimate pct by breaking things down into RISP & NONRISP and Late&Close & NONLate&Close (the OPS and OPS allowed in each case), I get some slightly higher estimates for the Royals winning pct.
Using the Late&Close regression, they would have about a .520 winning pct and using the RISP regression, they would have about a .525 pct. There probably is a bit of an overlap between the two situations (maybe 4.165% because usually RISP is about 25% of PAs and L&C is about 16.66%-multiplying .25*.1666 gets about .04165).
But perhaps combining the two together would get us to about a .540 winning pct. That would be 87.5 wins and that is pretty close to the 89 they actually got.