Vonn finished the icy course in 1 minute, 30.31 seconds, well ahead of Swiss teenager Lara Gut and Nadia Fanchini of Italy to win her second gold medal of the Worlds.
Gut turned in a 1:30.83, just ahead of Fanchini's 1:30.88.
Vonn, who placed first in the super-combined last week, attacked the course and turned in sizzling splits on the first two intermediates. She was fast enough at the bottom to edge Gut out of first place.
Gut has won medals now in two of her four World Cup downhills. She also won the silver in the super-combined.
The course was described by the International Ski Federation as being in excellent shape, but icy, after heavy snow forced postponement of the ladies' downhill on Sunday.
Defending champion Ana Person of Sweden lost a bit of control on the critical Virage Russi hairpin turn while enjoying a potentially winning run and wound up tied for ninth.
2014: The Year in Fashion [PHOTOS]
UPI Sports Results for September 19, 2014