Wilander reckons Andy shouldn't be too worried as Dimi is playing above his level just now and if it is a marathon match Andy is used to coping.
My opinion too. Murray needs to win at least one of the first two sets though. Dimitrov probably can't sustain this intensity for 4-5 sets, but if he gets to 2-0 he might be able to keep it going for one more set. You'd also seriously hope Murray will play better than he did at Wimbledon, although his level right now isn't far off that performance. Looks a bit rattled.
Should point out that my stream is a good 1-2 minutes behind and at the time of typing he had just gone 30-15 down. What an absolutely stunning backhand pass.