The 49ers opened as 13.5-point favorites at Caesars Sportsbook but closed as 10-point favorites. At other Vegas sportsbooks, the spread closed at 49ers -9.5.
Down 30-26 with two seconds left at their 22-yard line, the Cardinals attempted a lateral that led to a sequence in which the 49ers recovered a fumble for a touchdown. The NFL changed its extra-point rule in 2018 (in the offseason after the Minneapolis Miracle), so the 49ers did not have to line up to potentially kick the extra point after time expired, making the final score 36-26.
For Caesars, it was a "worst-case scenario," according to director of trading Jeff Davis.
"We needed the Cardinals to lose by more than 10 since no parlays lost and Arizona backers at more than 10 didn't lose," Davis told ESPN in an email. "San Francisco by four was no good, but by 10 was worse. We needed [the 49ers] by 11 or more."
The Cardinals built up a 16-0 lead in the first half and were winning 26-23 with 31 seconds left in the game before surrendering a touchdown and fumbling the kickoff to the 49ers. San Francisco ran four plays to make Arizona use its timeouts and gave the ball back to the Cardinals with six seconds left, setting up the ensuing touchdown.
"It just didn't work out [that] way, but I'm pretty sure some people in Vegas were happy," Cardinals receiver Larry Fitzgerald said of what went wrong on the final play.
The damage wasn't as bad at other sportsbooks.
"Our action was split fairly evenly between 49ers -10.5 and -10," Matt Chaparales, head of content at PointsBet, told ESPN. "Our line never touched 49ers -9.5, so a good chunk of clients survived and cashed their tickets while the rest had to settle for a tough push."
DraftKings told ESPN that 60% of bets and 61% of the handle were on the Cardinals, mostly at Arizona +10. The play didn't cause a big swing at the Westgate Las Vegas SuperBook.
The Cardinals were tied with the Green Bay Packers as the NFL's best team against the spread, at 7-3, entering Week 11. They fell to 7-3-1.
ESPN's Josh Weinfuss contributed to this report.