The Australian told BBC Sport: "I took the easy way out by starting on wet tyres and to be honest, I was scared of crashing.
"I didn't want to injure my foot any more than I have already, especially in my last race. You can see there were a lot of crashes today.
Amazing overtakes set up Marquez win
"My eyes were the size of dinner plates the whole race. With a couple of laps to go I decided to go for it and it's a fantastic way to end it. I want to thank all my supporters down the years."
With riders starting on different tyres, the first few laps were chaotic as Aleix Espargaro took a shock lead to become the first CRT rider to lead a MotoGP race.
Within a few laps it was clear that the slick tyres were quicker, and as riders came into the pits to change bikes Lorenzo was able to stay out and take the lead.
Lorenzo and Pedrosa, who lined up on wets before changing his mind on the warm-up lap and coming in to change tyres and start the race from the pit lane, pulled clear before Lorenzo's huge crash.
The Spaniard was trying to lap British rider James Ellison when he got off line, weaved several times before being catapulted into the air and landed on his head before coming to a stop.
Lorenzo on title-winning season
That left Pedrosa clear to win his seventh race of the season, while British rider Cal Crutchlow, who had been set for a best-ever finish of second, crashed out late on to give Nakasuga a place on the podium.
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