Josh Brown tied a league single-season record with his fourth winning field goal in the final minute, nailing a 50-yarder with four seconds left to give the Seahawks a victory.
Rookie defensive lineman Darryl Tapp returned Jay Cutler's first interception 25 yards for a touchdown and the Seahawks took advantage of five turnovers.
Seattle started its winning drive from its 14 with 2:31 left after the Broncos tied it at 20 on Cutler's 71-yard touchdown to fellow rookie Brandon Marshall, who broke three tackles on the play.
On third and 4 from his 20-yard line, Matt Hasselbeck found Nate Burleson for 16 yards. Brown, who missed from 40 and 53 yards in the first half but was good from 44, 23 in the fourth quarter, soon won it from 50 yards.
"Josh Brown's been clutch for us all season long," Hasselbeck said. "He's a great kicker."
Cutler, the last of the "Big Three" quarterbacks from the 2006 draft class to make his debut, met the same fate as Vince Young and Matt Leinart - a loss.
He looked like a raw rookie most of the night, but did show flashes of brilliance, such as his touchdown pass to Marshall.
Coach Mike Shanahan said he was pleased with Cutler's performance.
"I think he did pretty good for being his first game," Shanahan said. "I'm a little disappointed in myself. I think I put too much in the game plan for this being his first game."
NOTABLE: Denver lost linebacker Al Wilson to a sprained neck in the fourth quarter - Wilson was carted off the field - and kicker Jason Elam appeared to hurt his left leg on a fake field goal run just before halftime.
Seahawks 0 7 0 16 23
Broncos 3 10 0 7 20