Victory for the four-year-old, considered unlucky in several other big handicaps this season, was by far the biggest British success in the career of trainer Ismail Mohammed.
Murtagh kicked to the front on the 8-1 favourite two furlongs out and although his mount drifted across the track, he had enough in reserve to hold the late charge of Henry Candy's Code Of Honor (12-1) by a short head. The first two ended up in the centre of the track. Tres Coronas (25-1) was third on the far side and Graphic (16-1) fourth on the near rail.
Murtagh, who started training earlier this year, was top jockey at Royal Ascot and also won the King George and Haydock Sprint Cup this season. He said: "I had to commit a bit sooner than I wanted to and was in front half a furlong too soon.
"He drifted left and got a bit tired towards the end and I was glad that the line came in time. It was a brilliant performance with a lot of weight. He was a class horse in a handicap.
"I can't really believe it - you couldn't write it. I didn't have any ride in the Guineas, no ride in the Derby. I said to my wife going to Ascot, thank goodness we are training a few.
"Since Ascot, it has turned around. My life has been like that. When opportunities come your way, you have to take them. That is what I've been doing the last couple of months."
Mohammed said: "He's won a lot of races for us, but this was the one I wanted. Winning races like this can only be good for us. I want my team to get bigger and bigger. Educate will go to Dubai and we have a programme for him there."
Candy said of the runner-up: "It was just a little too firm for him early on, but once he kicked in he finished like a sprinter."
Paul Cole's Berkshire (11-8 joint- favourite) left bookmakers underwhelmed despite winning the Juddmonte Royal Lodge Stakes by a neck from fellow market leader Somewhat. Berkshire's performance at Royal Ascot in the Chesham was so breathtaking many expected victory by a bigger margin, given his clear superiority over the same rival at Ascot.
Jim Crowley looked confident aboard the winner, but ended up picking up a two-day whip ban (October 13 and 14).
Cole said: "It was quite an exciting race. [Berkshire] looked a bit green and had not run for a long time. It can be quite hard for two-year-olds on their first run back after a long time off. He probably won't run again this year. He's a big horse and next year is going to be his year."
Mick Channon's Ayaar (6-1) got off the mark for the season in the 1st Security Solutions Handicap in the hands of Ryan Moore, showing a fine attitude to see off the challenge of Mezzotint to win by a neck.
Channon said: "He has been his own worst enemy really as he won a Group Three in Germany last year and it has been hard for him this season. There's a three-year-old handicap at Ascot next weekend and we might have to run him there."
Amralah (100-30) completed a brace for Channon when he stepped up to a mile and a half with aplomb under Silvestre De Sousa in the Paul & Lesley Stevens Silver Wedding Anniversary Handicap. "He's had his problems, which is why you haven't seen him too much, but I think he could be a nice horse next year," the trainer said.
Mickael Barzalona was seen to good effect when timing his run to perfection on top weight Autumn Lily (9-1) in the Irish Stallion Farms Jersey Lily EBF Fillies' Nursery. Winning trainer Charlie Appleby said: "She's a filly who likes quick ground and she got a nice lead. We might look at a race like the Montrose Stakes [at Newmarket on November 2]."