With its back on the goal line, the defence answered the challenge.
The Seahawks stuffed Daryl Richardson on third-and-goal, and then caused Kellen Clemens to overthrow his intended target in the corner of the end zone on the final play of a nerve-wracking 14-9 victory.
"The defence did a tremendous job, coming up with a huge stop there," said Seahawks star Russell Wilson, who was sacked a career-high seven times.
The outcome capped a lousy night for St. Louis sports fans. The Cardinals lost 3-1 to the Boston Red Sox in Game 5 of the World Series, played just up Broadway at Busch Stadium.
"I'm proud of our guys," Rams coach Jeff Fisher said. "We felt like we had a chance."
Seattle (7-1) extended the best start in franchise history despite gaining just 135 yards, with 80 coming on Wilson's second TD pass to Golden Tate. It was the third-fewest yards in a victory for the Seahawks, and their seven first downs were the fewest in a win in franchise history.
"We were very fortunate," Seahawks coach Pete Carroll said. "Under the circumstances with a new quarterback, they did a great job. We just couldn't get going on offence. Fortunately, the defence hung together and gave us a chance to win the game."
Clemens finished with 158 yards passing in place of the injured Sam Bradford, but he also threw two interceptions. Zac Stacy ran for a career-high 134 yards to pace the Rams (3-5).
"It's not always going to be pretty," said Seahawks cornerback Richard Sherman, who grabbed his fourth interception of the season. "You have to be able to win ugly."
The World Series no doubt contributed to the stale atmosphere inside the Edward Jones Dome, where the announced crowd of 55,966 was in reality much smaller. Many of the fans who did show up wore Cardinals gear, and Cardinals-Red Sox highlights were shown on the big screen.
Greg Zuerlein staked St. Louis to an early lead with his first of three field goals, but Sherman's pick put the Seahawks in business. Seattle scored six players later, when Wilson hit Tate from the 2-yard line.
Zuerlein got the Rams within 7-6 late in the third quarter, but the Seahawks answered.
Wilson went deep down the sideline to Tate, who made an acrobatic leaping catch over Janoris Jenkins. Tate regained his balance and then mockingly waved at safety Rodney McLeod as he ran to the end zone, earning an unsportsmanlike conduct penalty.
"He just was so in the moment and just made an unbelievable catch," Wilson said. "You've got to give him credit for just attacking the football right there."
Zuerlein connected again to get St. Louis to 14-9, but he missed a 50-yard field goal in the fourth quarter. That proved to be critical because the Rams would have needed just another field goal from him on their final drive, rather than a touchdown, to steal the win.
They still had a chance after they took over at their own 3-yard line with just over 5 minutes left, and methodically marched down field. They had first-and-goal at the Seattle 6 with about a minute left, and Richardson carried the ball to the 2.
An encroachment call on Seattle put the ball at the 1, but Richardson was stuffed on third down and Clemens misfired on fourth down as the final seconds ticked off the clock.
"We needed 97 yards, we got 96," Clemens said. "There was such a great sense of resolve in the huddle as soon as I walked in the huddle. Everybody knew. Nobody really had to say anything. We gave ourselves a win at the end, but unfortunately we didn't make the play."
NOTES: Rams DE Robert Quinn had three sacks, all in the first half. ... Seattle had minus-1 yard of offence in the first quarter, and 38 yards at the half, its fewest since gaining 37 in the first half against Kansas City in 1998, according to STATS LLC. ... Seahawks WR Sidney Rice left late in the first half with a knee injury and did not return.