Murray has won 6 of their 8 previous matches. Their last one was in August 2015.Murray won in 3 sets on a hard court. In their 5 hard court matches Dimitrov has only failed to take a set once and that match had a tie break.
Dimitrov is having a decent season so far but lost to Zverev in Indian Wells and struggled against Delbonis in this tournament.
Miami is Murray’s second home and he is comfortable there. He will be sleeping in his own bed and have his own things around him rather than staying in a hotel room. That can make a big difference. He lost to Delbonis in Indian Wells so clearly isn’t at his best.
I can see this going to 3 sets with Murray coming out on top. Back Murray if he is broken first.