Matt Hasselbeck, who was active as the backup, warmed up on the field for about 20 minutes approximately two hours before kickoff. He threw a number of passes downfield before jogging back to the locker room while Whitehurst remained on the field throwing.
Seahawks coach Pete Carroll said all week they were planning for Whitehurst to start after Hasselbeck injured his hip last week at Tampa Bay.
Receiver Brandon Stokley (head) was the only injury-related inactive for Seattle. St. Louis had no players inactive who were listed on Friday's injury report.
Information from The Associated Press contributed to this report.