It was a rough start for Seahawks quarterback Sam Darnold.
Darnold was sacked for a 7-yard loss by linebacker Jaden Dugger on second down and was intercepted by Renardo Green on third down on a pass intended for Jaxon Smith-Njigba.
The 49ers needed only four plays to go 18 yards to the end zone.
Mike Evans caught a 13-yard pass to the Seattle 2 and scored on the next play.
It is his third touchdown of the season.
49ers quarterback Brock Purdy is 2-of-5 for 15 yards and a touchdown after going three-and-out with two incompletions on the first possession.