The final numbers confirmed what Fox feared.
Early returns indicated the San Francisco Giants' four-game sweep of the Detroit Tigers could bring in the lowest World Series ratings on record, and Nielsen confirmed the average of 12.7 million viewers was the smallest ever.
That is down 23 percent from 2011, and below the previous record-low of the 2008 World Series between the Philadelphia Phillies and Tampa Bay Rays (13.6 million viewers on average).
Last year's World Series won by the St. Louis Cardinals in seven games over the Texas Rangers averaged 16.6 million viewers.
Fox signed an eight-year deal earlier this month to extend its MLB television rights.
"This World Series gave us exactly what we expected: a top 10 show among all viewers and a top five show among hard-to-reach younger men," said Michael Mulvihill, senior VP of programming and research, Fox Sports Media Group. "It's important for us to remain focused on the Series relative to today's competitive environment rather than bygone years. The World Series remains a powerful force in primetime and we're fortunate to have the Fall Classic for at least nine more years to look forward to."