The 1978 Red Sox had a great team, with 4 future HOFers and 2 borderliners (Tiant and Evans).
They started 62-28 (.689) and finished 37-36 (.507).
They played the Yankees 8 times from September 7 to October 2 and lost 7 of them.
If you want to characterize this as something other than a collapse, hey, no one can stop you.