Baldwin sustained an ankle injury during the first half and originally was deemed questionable to return. He later was downgraded to out.
Smith went down when he made a hard, helmet-first tackle on 49ers return man Ted Ginn Jr. on the opening kickoff and was helped off the field. The Seahawks later announced Smith wouldn't return to the game.
The teams came into the divisional game tied for first place in the NFC West with 4-2 records.
The Associated Press contributed to this report.