Scot Murray, 28, was 3-1 up in the third set but told BBC Sport "a lot of unforced errors crept into my game".

Bulgarian Dimitrov won the last five games and Murray will now return to Europe for the clay-court season.

Earlier, Johanna Konta became the first British woman to reach the quarter-finals in Miami, but Heather Watson lost to Simona Halep.

Disappointing loss mystifies Murray

Murray made 55 unforced errors against Dimitrov, smashing his racquet as he slipped 4-0 down in the second set before losing his last three service games in the decider.

"Grigor played some good stuff too, but to lose your serve three times in a row from that position is obviously disappointing," said Murray.

The Scot had enjoyed plenty of practice in Miami - where he has a home and does his off-season training - after losing early in Indian Wells.

"It's disappointing, that's for sure," he said. "I had time to prepare on the court and get used to the conditions, but I wasn't able to get on a good run."

Murray's wife Kim and new daughter Sophia had travelled to Miami and the family will now spend some time together before he returns to the practice court.

"I would imagine we'll stay for a couple of days and then head home, try to get on the clay as soon as I can and get ready for Monte Carlo," said the world number two.

Another landmark for in-form Konta

Konta, 24, kept British hopes alive with a dominant performance against Romania's Monica Niculescu, winning 6-2 6-2 to set up a quarter-final against Victoria Azarenka.

"I know it was 6-2 6-2 on the scoreboard but it felt like we had a lot of close games and I had to work hard for every single point," Konta told BBC Sport.

Asked about becoming the first British woman to reach the quarter-finals, she added: "It's a wonderful thing to have on paper and for other people to recognise, but I am very much in the moment in this tournament and it's not over for me."

Watson hampered by injury

Watson lost 6-3 6-4 to fifth seed Halep after letting an early 3-1 lead slip against the Romanian.

The 23-year-old Briton played with a strapping on her thigh to protect a muscle injury.

She said: "I felt fine going into this match but then tweaked it again and became overly aggressive going for stuff you shouldn't usually go for playing against Halep.

"I ended up paying the price, missed a few too many and was pretty inconsistent."

World number one and defending champion Serena Williams is out after losing 6-7 (3-7) 6-1 6-2 to Russian 15th seed Svetlana Kuznetsova.

(BBC)