The person that is supposed to step up and lead this team is the coach. If the players are have systematic trouble executing in a particular fashion or in a particular part of the game, it generally means one of two things. First, the players need to be changed. Second, for whatever reason, whether his fault or not, the coach is having trouble correctly instructing and motivating the players.
It is now four in a row on the road. You can blame the players all you want, but these are the same players that are great at home. Now you could argue in response that by the same logic Doc is also a great coach at home. However, presuming that you are not willing to say these players are not hard workers, etc., etc., it is fundamentally the job of the COACH to motivate the players in difficult situations.
Doc seems to be a great front-running coach, but he just seems terrible in difficult situations. But that is just my perception.
p.s. Is there any data on the Celtics record in close games in the Doc era (yes, I realize Game 3 was not close) compared with other coaches in the same time period?