ATLANTA — For the first 30 minutes, the Seattle Seahawks looked like Super Bowl contenders. Over the last 30 minutes, they looked like playoff pretenders. But in the end they did just enough to hold on.

Seattle used a dominating first half and a crucial defensive play by rookie safety Marquise Blair to hold off the moribund Atlanta Falcons 27-20 on Sunday at Mercedes-Benz Stadium.

The victory allowed Seattle (6-2) to keep pace in the NFC West — the San Francisco 49ers and Los Angeles Rams both won Sunday — but after racing out to a 24-0 halftime lead, the Seahawks found themselves on the back foot the entire second half, with Blair’s forced fumble on Atlanta running back Devonta Freeman at the goal line looming large in the final result.

“I thought we were lights out in the first half,” Seahawks quarterback Russell Wilson said. “In the second half, we have to be better. We have to find ways to be better and be more sharp. If we want to go where we want to go, we have to be great every quarter.

“But I’m fired up, 6-2 is great. The reality is we have places where we’re trying to go and we can continue to be better.”

Facing an Atlanta team in disarray — the Falcons came into the game 1-6 with speculation swirling about coach Dan Quinn’s future — the Seahawks seemed to be driving the final nail in Quinn’s coffin when they bulled past the Falcons in the first half. A dominant run game featuring the duo of Chris Carson and Rashaad Penny (a combined 145 yards on 28 carries in the game) laid the foundation, and quarterback Russell Wilson (14-for-20 for 182 yards and two touchdowns) was back to his efficient self after an off game against Baltimore last week, connecting twice with rookie wideout DK Metcalf for touchdowns.

But the game took a dramatic turn in the second half as Atlanta out-gained Seattle 355-82 over the final two quarters. Journeyman Matt Schaub, thrust into the spotlight as franchise quarterback Matt Ryan (ankle) missed his first start in 10 years, used quick releases and screen passes to carve up the Seattle defense as he threw for 460 yards.

“I’ve said for a long time, you can’t win the game in the first half, but that’s what that was,” Seahawks coach Pete Carroll said.

“I didn’t do a good enough job,” Carroll added, taking responsibility for his team’s second-half display. “Obviously we went out there and looked like we were a totally different team. There’s a lot of things — I’m not going to go into it — that take place when you don’t play well, and I have to do a better job of making sure that doesn’t happen.”

It was a big play by Blair that ultimately proved decisive. Early in the fourth quarter, with the Falcons having cut the difference to 24-11, Atlanta drove the length of the field and was on the verge of scoring. Schaub completed a pass to Freeman, and as Freeman stretched the ball toward the goal line, it was tipped out of his hand by Blair, with linebacker Bobby Wagner scooping up the fumble. Freeman claimed he was down before the ball popped out, but the play was upheld after video review. The Seahawks then went on a seven-minute drive that ended with Jason Myers’ 54-yard field goal, and that created a margin too large for Atlanta to overcome.

“He’s tough, man,” Carroll said of Blair. “He showed his hitting ability, every game he’s played he’s made some hits that jump out. That’s what we loved about him when we drafted him, and he continues to show that he has a real knack for firing on people, and we love his style.”

Seattle was almost flawless in the first half, scoring on four of its five possessions. That was particularly the case in the second quarter, when the Seahawks scored three straight touchdowns to take a 24-0 lead.

The first TD came after hard running by Penny and Carson set up Wilson, who used a quick count to find Metcalf wide open on a slant for a 4-yard touchdown. Then Seattle cashed in on linebacker Mychal Kendrick’s interception as Carson and Penny again carried the load, with Carson finishing it off by getting around the right edge for a 1-yard score. Finally, the Seahawks got the ball back following a missed Atlanta field goal with 2:29 remaining, and Wilson again found a wide open Metcalf, this time for a 2-yard TD.

At that point it appeared the Seahawks could coast home, but the Falcons had other ideas. Atlanta received the ball to start the second half and proceeded to drive 75 yards on eight plays, with Brian Hill darting through the defense for a 23-yard touchdown run. A successful two-point conversion made it 24-8.

Seattle responded with two three-and-outs, with the Falcons converting a field goal in between. Then Atlanta, starting at its own 14, drove the length of the field again against a soft Seahawks defense, and the Falcons were on the cusp of the end zone when Blair made his saving play at 12:57 of the fourth quarter.

After Myers’ field goal made it 27-11, the Falcons knew they needed two touchdowns and two two-point conversions to tie the game. They got the first TD when Schaub took Atlanta 75 yards in just 2:45, threading a pass to tight end Austin Hooper for a 1-yard TD. However, Wagner came up with a huge pass break-up on the two-point try to keep it a two score game at 27-17 with 3:08 remaining.

Atlanta had an unsuccessful onside-kick try, and Seattle had a chance to salt the game away. However, a pair of short runs combined with a penalty forced the Seahawks to punt, giving the ball back to the Falcons with 2:41 remaining. Atlanta again drove the field and chose to take Matt Bryant’s 37-yard field goal with 1:17 remaining to leave some time on the clock for a potential final drive. However, the Falcons’ onside-kick attempt bounced out of bounds before it reached 10 yards, and Seattle was able to breathe a sigh of relief.

Extra points

Wagner finished with five tackles, giving him 988 for his career and making him the all-time leading tackler in Seattle franchise history, surpassing the previous record of 984 set by Eugene Robinson. … The Seahawks lost starting center Justin Britt in the first quarter to what appeared to be a serious injury to his left knee. Britt was replaced by Joey Hunt. After the game Carroll said tests need to be done, but he feared it was an ACL tear. … Seattle welcomed a pair of starters back from injury as left tackle Duane Brown (biceps) and defensive end Ziggy Ansah (ankle) returned to action. First-string safety Bradley McDougald (back) also was back, but played sparingly. Cornerback Tre Flowers (neck) was inactive.