With its back on the goal line, the defense 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 defense did a tremendous job, coming up with a huge stop there," said Seahawks quarterback Russell Wilson, who was sacked a career-high seven times.
"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 offense. Fortunately, the defense hung together and gave us a chance to win the game."
"It's not always going to be pretty," said Seahawks cornerback Richard Sherman, who made 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 Red Sox-Cardinals highlights were shown on the big screen.
Greg Zuerlein staked St. Louis to an early lead with the first of his three field goals, but Sherman's pick put the Seahawks in business. Seattle scored six plays 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 again.
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."
Tate apologized after the game, NFL.com reported.
"That was immature of me. Hurt my team. I've gotta stay composed. ... Act like I've been there before," Tate said, according to the website. "I gotta apologize to our special teams. I put them in an awkward situation, but more happy to get up and learn from it and move forward."
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 3-yard line with just more than five 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 [chance to] win at the end, but unfortunately we didn't make the play."
Rams DE Robert Quinn had three sacks, all in the first half. ... Seattle had minus-1 yard of offense in the first quarter and 38 yards at the half, its fewest since gaining 37 in the first half against the Kansas City Chiefs in 1998, according to STATS LLC. ... Seahawks WR Sidney Rice left late in the first half with a knee injury and did not return.
The Associated Press contributed to this report.
What's trending in the NFL: Deadline on Peyton Manning's decision; Cam Newton says he's a 'sore loser'
Recapping Tuesday's top stories, which include the Broncos needing to know whether Peyton Manning is retiring by March 9 and the Panthers QB defending himself for his action after the Super Bowl.
President Barack Obama calls Broncos coach Gary Kubiak and LB DeMarcus Ware to congratulate them on their Super Bowl 50 victory over the Panthers.
To Greg McElroy, not jumping on the loose ball after his fourth-quarter fumble meant Cam Newton gave up on his Panthers' chances in Super Bowl 50.
The Patriots' place-kicker spent Tuesday visiting sick kids in a Boston hospital, taking questions on football and life.
Rams receiver Stedman Bailey, who was shot in the head in a November incident, recently posted a YouTube video updating his recovery and confirming his hope to return to the NFL.
Breaking down the Arizona roster, position by position, by oldest player, youngest player and average age.