After a lacklustre display in his previous round at Flushing Meadows, Murray insisted he would have to improve to overcome an in-form Dimitrov and he certainly kept his promise.
The 29-year-old was broken only once in the whole match and produced the fastest serve of his career, at 141 miles per hour, to win the opening set.
“I played extremely well, tactically I played a good match,” Murray said.
“It’s definitely up there, I played well today, made very few unforced errors and made it tough for Grigor.”
On his record-breaking serve, Murray added: “I served one at 145 in San Jose once but the next day they recalibrated the gun because it was completely wrong.
“Tonight’s was the fastest serve I’ve hit. The other one was here at the US Open, 138. I think it was lucky. I only did it once. I’m not expecting to do it again.”
If this hammering had come in the earlier rounds it perhaps would have been less impressive but Dimitrov is ranked 24th in the world, beat Murray in Miami earlier this year and ousted world number three Stan Wawrinka at Cincinnati last month.
The talented Bulgarian has enjoyed a resurgence under Murray’s former coach Dani Vallverdu but any confidence gained may have been shattered in what was, at times, a humiliation.
Murray is in the midst of his own golden patch with Ivan Lendl, under whom he has still only lost one match, but even in his runs to winning Wimbledon and the Olympics, it is hard to recall a more convincing performance.
“His belief is higher than it’s ever been,” seven-time grand slam champion John McEnroe said on ESPN. “That’s what makes him even harder to beat right now.”
Dimitrov ripped a backhand pass to open up two break points in the very first game but that was as good as it got for the 25-year-old who, after 1-1, lost nine games in a row.
Murray began his streak as he often does, by making his opponent play one more ball. Twice in one game he forced Dimitrov to take two smashes to finish the point, and the second time his willpower was rewarded as the Bulgarian thrashed his effort into the net.
Up one break, Murray grabbed another, and a sublime set of tennis was given a final flourish, an ace, and at 141 miles per hour, Murray’s fastest of his career. No player left in the tournament has served faster here.
Murray was now in full flow. He broke in the first game of the second with a whipped forehand winner, and again in the third to lead 3-0, as a sleepy crowd began to wonder if Dimitrov would ever get on the board.
He did, with a break, but Murray broke back instantly, prompting his opponent to attempt his most ambitious shot of the night - a flying right-foot volley, kicked through the air in frustration. He failed to make contact.
By the start of the third set, even Lendl was getting fidgety as the Czech stretched his legs and temporarily watched standing in one of the entrances.
Murray left his best until last, as Dimitrov unleashed a stinging backhand pass and somehow his opponent read it, racing across and volleying home a winner.
Rain began to spit down on court before the final game, but nothing could halt Murray’s progress as a wide forehand confirmed Dimitrov’s exit in a brisk two hours and one minute.