Tomac finished in eighth place and now trails series leader Dungey by 9 points – 341 to 332 – with the final race in Las Vegas to go in the race for the series title.
Tomac entered the race at MetLife Stadium with a 3-point lead, after winning nine of the past 12 races and rising to the series lead for the first time in his Supercross career.
He had a hard time in his heat race Saturday, finishing fourth and 7 seconds behind winner Jason Anderson of Husqvarna, and Marvin Musquin and David Millsaps. Meanwhile, Dungey cruised in his heat race to a 7-second win over second-place Blake Baggett.
In the main event, Tomac finished the first lap in third and briefly took the lead after Anderson crashed in the second lap and dropped to eighth.
In the third lap, however, Tomac crashed hard after tucking his front wheel in a rutted curve. As he struggled to restart his Kawasaki, 14 riders passed him, forcing Tomac to try to battle back from 15th place.
Two-thirds of the way to the finish line, Tomac had another mishap, landing hard on a bump and appearing to stall his bike as he briefly left the course and dropped to 12th place. He charged back in the final few laps to finish eighth, picking up just 13 points for the race.
Dungey, racing in second place behind Musquin for the second half of the race, overtook his KTM teammate in the final lap as Musquin went slow and wide after exiting a curve. Anderson finished in third.
By finishing first instead of second, Dungey added three points to his overall lead over Tomac.
Fans in the stadium reportedly booed as Musquin appeared to let his teammate by, and a debate quickly started on social media. In a Fox poll on Twitter after the race, 86 percent of respondents indicated that they thought Musquin let Ryan pass, and 14 percent said they thought Musquin made an honest mistake.
On Twitter, racing veterans Juan Pablo Montoya and Ricky Carmichael weighed in with their opinions.
“That’s what u call team orders,” Montoya said in a tweet.
“That was a good business decision,” Carmichael tweeted.
In the post-race press conference, Dungey and Musquin denied that the last-lap pass was part of a team tactic.
Dungey now leads Tomac by 9 points. The final race is next Saturday in Las Vegas.