The popular Italian claimed the prestigious contest for a record fifth time when winning aboard Enable at Chantilly last season, adding to his previous triumphs aboard Lammtarra (1995), Sakhee (2001), Marienbard (2002) and Golden Horn (2015).
Having missed much of the season through injury, Enable had endured a far from ideal preparation for her Arc defence.
But Dettori - riding in the race for the 30th time - had his mount in the perfect position throughout and she had just enough in the tank at the finish to deny the fast-finishing Sea Of Class by a neck.
Dettori said: "It was my 30th Arc and I was more nervous than ever, not to mention excited, but in the race I found myself in a fantastic spot.
"In the false straight the leaders came back and I knew then we were in business.
"I waited as long as I could and at the 300 (metre pole) she showed her trademark turn of foot.
"It was almighty pressure on all of us - everybody wanted her to win and I had to get it right. It would be very naive to say that I wasn't nervous."
Enable had only run once since her victory last season, at Kempton on the all-weather last month.
Dettori added: "What a genius John Gosden is, to win an Arc with that interrupted preparation.
"In the last 50 yards we were on our hands and knees, I was trying to squeeze everything we could out of her and we got there."
Paying tribute to his jockey, Gosden said: "He gets himself up for these occasions and rides to a level that is way beyond what most people can ride to.
"He rode a gorgeous race, but he thought in the last 100 metres 'I'm in trouble'."
