He was initially fast in practice but after slipping back in qualifying said: "I'm disappointed in myself, but it is what it is.
"I'm pushing out there and trying to find the limits in a fast-forward motion. We'll just come back and have a go tomorrow."
Dixon meanwhile has seen a 117-point series lead whittled back to 32 but he is hotly favoured to win the IndyCar title, and even more so after Newgarden missed out on an extra pole position point.
"Josef starting 8th…that definitely helps us a lot. If they're not making top three, we don't have to do anything," Dixon said.
Newgarden was frustrated with himself and his car.
"It makes our programme a little harder for tomorrow but we're still going to try for the win," he said.
"We can win (the title), we just made it harder on ourselves."
Australian Will Power won his 62nd pole position - five short of Mario Andretti's record - for the 14th and final race of the season.
The 14-turn temporary course, which includes part of an airport runway, will have up to 20,000 spectators. They are required to wear masks and socially distance, and will be temperature checked, because of Covid-19.
The race was postponed and seemingly cancelled earlier in the year, and Dixon said just getting to the IndyCar finish line was a "major victory" during the pandemic.
"It's been such a bizarre year, a year I'll definitely never forget, no one else will really," he said.
"There will be standout moments you'll reflect on like walking out of Gasoline Alley on race day and seeing nobody. A polarisation of what's normal.
"We have to be thankful for the situation we're in."
