It was a ride of sheer quality and one that broke the five-year stranglehold on the event of the record 23-times winner, Joey Dunlop, but it came in a race that once again underlined the dangers of riding on this torturous circuit with its high-speed lap of the island, through towns, villages, over Snaefell mountain and along country roads lined by stone walls.
McGuinness had already raced through the Greba Castle section of the course, but Dunlop was just entering it as he saw his fellow Ulsterman, James Courtney, crash, with his Aprilia slamming into a wall.
"I saw it all, right in front of me - maybe he touched the kerb and that threw him, but it was very scary," Dunlop, the 47-year-old Ballymoney publican, said. "It totally de-tuned me. I am disappointed to have finished fifth, and just hope that my fortunes improve later in the week."
Courtney was air-lifted to hospital in Douglas with suspected fractures as the race continued. McGuinness shattered the lap record for the first time, at 117.88mph, and then, to show it was no fluke, next time around, he stretched his advantage to 21sec with a lap of 118.29mph.
"I decided to go for it from the off, and was running first on the road on the second lap - in fact if I had got past them earlier, my speed would have been better as they were holding me up," said McGuinness, who maintained the pace in the second half of the race, after a brief re-fuelling stop, easily heading off the challenge of the Yamaha rider, Jason Griffiths, with Gavin Lee third.
"Winning is a real delight - we came over here to enjoy ourselves," McGuinness said. "There was no pressure to go out and win, but for me it is a dream come true. I've been coming to the TT as a spectator since 1982 and I just hoped that one day I could get the chance to win. I can hardly believe that it has happened."
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