The American was 220 points ahead of countryman Trey Hardee through five events Wednesday.
Canada's Damien Warner was third, 55 points back of Hardee.
"I feel great. I made it a goal to just come out and have fun and I knew the score would just come," said the 22-year-old from London, Ont. "My hurdles are strong, 1500 metres is strong, discus is getting better and I'm consistent in the pole vault.
"The score and placing after day one doesn't surprise me, I have very high expectations of myself."
Eaton began the morning by breaking Bill Toomey's 44-year-old record in the 100-metre dash. He ended it with a solid performance in the 400. In between, Eaton finished first in the long jump, 11th in the shot put and second in the high jump.
The 24-year-old from Oregon has the spotlight on him after breaking the world record at the U.S. trials in June when he finished with 9,039 points. His mark eclipsed Roman Sebrle's 11-year-old record by 13 points.