The first half of the Vikings’ shocking 27-6 loss to the Bills on Sunday had to be one of the worst in Kirk Cousins’ career, and it had less to do with his ability than with the offensive line’s poor blocking. The group remains a big liability for this team.

There’s just no way of understanding how the Vikings could come out so flat against a team considered one of the worst in the NFL and 16½-point underdogs on the road at U.S. Bank Stadium.

According to the Las Vegas sports books, the outcome was tied for the fourth-biggest upset in NFL history and was the largest upset since 1995, when Washington won in Dallas as a 17-point underdog.

If you ask me, the Vikings overlooked the Bills with a big game coming up against the Rams in Los Angeles on Thursday night. The game played out like a bad dream.

In the first half, Cousins went 9-for-14 for 44 yards, fumbled twice and was sacked three times.

And you have to wonder if one play early might have changed the whole course of the game.

The Vikings appeared to force the Bills into a three-and-out in the first series of the game after linebacker Eric Wilson sacked Bills rookie quarterback Josh Allen on third down at the Buffalo 24-yard line. But nose tackle Linval Joseph was called for a lowering-the-head penalty that cost the Vikings 15 yards and gave the Bills a first down.

The Bills scored seven plays later on Allen’s 10-yard TD run, and the Vikings never got into any kind of rhythm after that.

Frazier dominates

It had to bring some real satisfaction to former Vikings head coach and current Buffalo defensive coordinator Leslie Frazier, who was awarded the game ball by Bills coach Sean McDermott after the game for his defensive schemes in shutting down the Vikings offense.

“It’s great for our team and it feels really good to get a win,” Frazier said. “It is not a lot of fun to be 0-2, so getting a win on the road against a good team feels good.”

Cousins said the Bills defense really changed the rhythm of the game by recovering two fumbles on two sacks in the first quarter.

“You can’t turn the ball over and give their offense a short field,” Cousins said. “We asked too much of our defense having to be out on the field so much, very little time of possession for us. We need to convert third downs and stay on the field to help give them a breather and allow them to stand up when they’re out there.”

Cousins praised the Bills defense and said he knew the Bills were formidable despite their poor start this season.

“Great defensive front, great defense, well coached, great scheme,” Cousins said. “They have legitimate players at a lot of positions, and they showed that. They played a really good game defensively.”

Did he think there was any part of the Vikings’ mind-set during the week that had them overlooking Buffalo heading into the game?

“I don’t think so,” Cousins said. “I think we have played long enough in the NFL to know how hard each game is. I have played against teams that finished 1-15 and they don’t feel any different than the team that finished 15-1 for much of the game. You may win, but it’s two or three plays you can point to that ultimately [went] your way and it could have been a loss. … Those of us in the league understand that it is an absolute grind every single week and it will always be that way.”

Field position was one of the biggest reasons the Vikings were undone Sunday.

Buffalo started its second drive on the Vikings 15-yard line following a sack and Cousins’ fumble. Its third drive started at the Vikings 25-yard line after another sack and fumble by Cousins.

Those two drives resulted in 10 points.

Like Cousins said, the time of possession in the first half made it impossible for the Vikings defense. The Bills had the ball for 20 minutes, 55 seconds in the first half; the Vikings had it for 9:05.

The total yardage in that half told the story: 245 yards for the Bills, 46 yards for the Vikings.

Allen takes over early

Allen, the No. 7 overall draft pick out of Wyoming, contributed an unexpected performance.

Last week in a 31-20 loss against the Chargers, Allen completed 18 of 33 passes for 245 yards with a touchdown and two picks. He didn’t start in a 47-3 defeat against the Ravens in Week 1 and completed six of 15 passes for 74 yards. His quarterback rating coming into the Vikings game was 61.0.

But on Sunday he controlled the ball and the game against a great Vikings defense.

He completed 11 of 18 passes in the first half for 168 yards and a touchdown and ran the ball seven times for 37 yards and two scores.

Coming into the game, defensive coordinator George Edwards had said Allen’s scrambling ability was going to be a big test for the Vikings, and that turned out to be true.

And while the stat book says the Vikings threw for 278 yards compared to 164 for the Bills, most of the Vikings’ yards came in the fourth quarter when the outcome was out of reach.

Cousins said of Allen, “I thought he played a great game — protecting the football, and they moved the football.”

Run game disappears

The absence of Vikings running back Dalvin Cook clearly had an impact on the rushing totals, which favored the Bills 128-14. The Vikings never established any kind of running game once the Bills got up big.

This was the second-worst rushing game in Vikings history. They had a worse day in 1996 when they carried the ball 14 times for 11 yards in a 15-13 loss on “Monday Night Football” against the Bears.

There’s no doubt that falling behind 24-0 meant the Vikings had to throw the ball more, but this was really a bad showing for the Vikings offensive line and their running game.

Only 11 times in team history have the Vikings rushed for 50 yards or less and allowed four sacks. And two of those four sacks Sunday led directly to Cousins fumbles in the first half.

Yes, Cousins was never able to get comfortable in the pocket and it was night and day compared to how the line protected in the first two weeks of the season, when Cousins was sacked only twice.

Now the Vikings will have to quickly regroup to face the Rams on Thursday, who have been dominant early in the season and crushed the Chargers 35-23 on Sunday.

If the Vikings lose that game — and they will be underdogs — they could be looking at a 1-2-1 start to a season that began with Super Bowl aspirations.

Sid Hartman can be heard on WCCO AM-830 at 8:40 a.m. on Monday and Friday and at 9:30 a.m. on Sundays. E-mail: shartman@startribune.com