This may have been the game you went to:
Boston Red Sox vs New York Yankees
May 27, 1991
Gray and Reardon both pitched. Barfield and Hall each had 2 home runs. Yankees win 6-5. Reardon got the lost for the Red Sox after giving up a home run to Hall in the 9th. Darwin started for the Red Sox.
I couldn't find many rain delays over 5 hours, so this may be one of the longest I presume
Link to Boxscore