Play-by-play announcer Tom "Hammy" Hamilton stated that Cody Allen asked manager Terry Francona to give Andrew Miller the 9th to help decrease Miller's workload for the time being. Allen worked the 8th inning during the Tribes' last two games.
It's not often a reliever volunteers to give save opportunities to his teammate, but that's exactly what's happening here. It'll be interesting to see how long this lasts as we have no clue if this will be for a week or for a month. In any case, it's far too early to panic and chances are, things will go back to normal once Francona feels Miller is better rested.