Andy Murray admitted he "struggled physically" during Sunday's Miami Open final defeat to Novak Djokovic, his seventh straight loss to the world No.1.
Djokovic overcame Murray in both the Australian Open final and the semi-finals at Indian Wells a fortnight ago and, for the second time in their last three meets, the British No.1 failed to register a game in the deciding set.
"I struggled physically," Murray said after his 7-6(3) 4-6 6-0 defeat, which sees him move back into the world's top three. "I don't think that I can do a whole lot more to get in much better shape. I'm training as best as I can. I can try to do more, but I do push myself hard."
Despite failing to secure a third Miami crown, Murray was optimistic on his performance and feels he is beginning to close the gap to his old foe - but, for him, fitness remains the biggest difference.
"There were a lot more positives than the match in Indian Wells," Murray added via the ATP's official website. "I felt like I did many things better. I made the match a lot harder for him. He might say otherwise, but I think I made it physically a much harder match for him.
"I felt like I was going for my shots a little bit more. I did pretty much all of the things that I wanted to do tactically on the court, so I felt like I played a good match tactically.
"I obviously know that Novak is a very fit guy, and sometimes in these conditions has struggled a little bit in the humidity. He handled it extremely well today and deserved to win the match because of that.
"He serves well, he runs well, he moves exceptionally well. Physically he's in great shape; he hits the ball well off both sides. He does most things on the tennis court well. That's why he's the No. 1 player in the world just now. In terms of game wise, I feel like in a couple of the matches we played this year, I feel like I've been able to hang with him, but just not quite for long enough, unfortunately."
Djokovic, though, insisted he would be taking nothing for granted after winning his fifth Key Biscayne title and becoming the first player to complete the Miami-Indian Wells double for a third time.
He said: "I'm trying to enjoy the moment and also utilise this time of my career where I'm probably playing the tennis of my life, and I'm feeling confident and physically fit.
"I'm trying to use that. That's what I'm thinking about right now ... I am aware that this cannot go forever. There is going to be eventually a change of generations, some players that are going to start playing better and be stronger."