On a Monday night at Soldier Field last month, when the Vikings won their third straight division game while holding the Bears without an offensive touchdown, the notion they could rebuild their defense on the fly, through lost preseason games and injured Pro Bowl players, might never have seemed more real.

The Vikings limited the Bears' moribund offense to 149 yards that night, knocking playoff nemesis Nick Foles out of the game and sending a head coach they hadn't beaten (Matt Nagy) in search of answers.

Mike Zimmer, the defensive architect who'd smirked at preseason expectations of a drop-off in 2020 and declared in August, "I've never had a bad defense — ever," had his team surging back toward a postseason bid with a group of young defenders that appeared on the way to proving him right.

He celebrated in the locker room that night by pointing out how quarterback Kirk Cousins had toppled a popular narrative with his first Monday night win and asking his team, "You like how this tastes? You like that?" with a smirk as he deadpanned his way through the quarterback's catchphrase.

There was no such revelry in the home locker room at U.S. Bank Stadium on Sunday, when the team the Vikings pummeled in November had 210 yards by the end of the first half. Instead, asked about running back Dalvin Cook's comments the Vikings' offense needed to take a long look at itself, Zimmer quietly responded, "The defense has to look in the mirror, too."

These Vikings might not be far from an extended opportunity for self-reflection, after a 33-27 loss to the Bears that put their postseason chances in dire condition.

The Vikings are now 6-8, after back-to-back losses to the Buccaneers and Bears stripped them of their playoff leverage before a must-win Christmas Day game against the Saints. On Sunday, the onus for their home loss to the Bears — their third in a row and their second in a must-win game — lay on their defense.

BOXSCORE: Chicago 33, Vikings 27

After an opening three-and-out, the Bears did not punt again, finding the answers they'd need for a depleted Vikings defense in the form of running back David Montgomery (who ran 32 times for 146 yards and two scores after missing the first game with a concussion) and re-installed starting quarterback Mitchell Trubisky.

He completed 15 of his 21 passes for 202 yards, making enough big throws to offset his one crucial mistake and adding 34 yards on scrambles. Chicago built a 20-7 lead at halftime, and then scored three times on four second-half drives that reached Vikings territory.

"The last time we played them they didn't score a touchdown on us defensively. And this week we couldn't slow them down," Zimmer said. "Didn't do a good job on the bootlegs, didn't do a good job in the run game. That was really disappointing."

Photo gallery: Vikings lose in home finale

The baseline requirement for the Vikings to reach the playoffs is for them to win their final two road games, on Friday in New Orleans and Jan. 3 in Detroit.

They will then need to root for help against the Cardinals from the 49ers and the Rams, both recent sources of bitter Vikings losses. And, if the Bears win in Jacksonville next Sunday, the Vikings will require help in Week 17 from their most bitter rival, the Packers.

"It's certainly not where we wanted to be," said Cousins, who threw for 271 yards and two touchdowns before his final-play Hail Mary was intercepted. "You look back and think about some really tough losses on one play here or there throughout the season that you know you're so close. That's why when you prepare all week and you're in the game you feel that intensity and intention on every snap because you know that it really is one snap that can make the difference between a win and a loss and going to the playoffs and not going to the playoffs."

The Vikings began the game without Eric Kendricks for the third straight week, and struggled to handle a Bears team that has recommitted to its running game since Trubisky replaced Foles and Montgomery returned after the bye week. Chicago had 10 runs of eight yards or more, including five on a 76-yard drive in the second quarter.

That allowed the Bears to keep Trubisky's workload relatively light, as the quarterback was able to target Allen Robinson in one-on-one coverage several times and use his feet to pick up three first downs.

The Bears put themselves within range of a touchdown that could have sealed the game in the fourth quarter after Robinson gained 37 yards on a deep over route against Chris Jones and a balancing act to keep his feet for more yards in almost the same spot where Stefon Diggs did it in the playoffs against the Saints.

Then Trubisky made one of the mistakes that have pockmarked his career. He floated a third-down throw into the back corner of the end zone, trying to hit J.P. Holtz behind both Jeff Gladney and Cameron Dantzler, who had returned to the game from an injury in time for his second interception of the year.

It gave the Vikings, trailing 30-27 with 2:57 left, an opportunity to tie the game with a field goal.

The Vikings used that chance to gain nine yards on three plays — two runs and a pass — to Cook. Then on fourth-and-1, they opted for play action that ended with Cousins backpedaling from Brent Urban and throwing a pass that fell short of Tyler Conklin with Khalil Mack in coverage.

"It was a bootleg, wanting to sell the outside zone," Cousins said. "And we had the bootleg right, but we had the defensive end there kind of in a bind where he either has to play me or play our slide route. But it was the next player inside, the defensive tackle, who was able to play up the field. And then I had to sink with a lot of depth to run away from him.

"In hindsight, I was talking about plays you agonize over, I think back even as I'm retreating, could I have ripped it to Justin [Jefferson] over the middle? Could I have thrown a ball over Mack to Conklin? Those are the things you think about after the play.''

Cousins got one more chance to win the game after a Bears field goal. With less than a minute to go and no timeouts, he hit three straight passes to move the Vikings to the Bears' 40. But the Vikings needed 20 seconds between plays before Cousins could spike the ball with 10 seconds to go. He hit Jefferson for a seven-yard gain with seven seconds left, and had time for one throw into the end zone.

The Hail Mary was tipped, then intercepted by Sherrick McManis to end the game.

"We're disappointed," Zimmer said.

Barring two wins and a lot of help, they're two weeks from being done.