CHICAGO -- Minnesota Vikings quarterback Case Keenum practiced with his teammates for most of the week without knowing what his role would be against the Chicago Bears.

"That's something I tried not to think about," said Keenum, who started the previous three games but returned to a backup role Monday night against the Chicago Bears. "I tried to approach the week like I was starting. I think that helps when you're called upon and you need to step in."

The strategy paid off as Keenum came off the bench to lead the Vikings to a 20-17 win over the Bears on Monday night. Kicker Kai Forbath kicked a 26-yard field goal with 12 seconds remaining for the go-ahead score.

Minnesota (3-2) earned its first road win of the season.

Bears quarterback Mitchell Trubisky completed 12 of 25 passes for 128 yards and a touchdown in his NFL debut. He threw an interception to Vikings safety Harrison Smith deep in Bears territory to set up Forbath's winning field goal.

Chicago (1-4) dropped its second consecutive game.

"We can't put him in those positions," Bears wide receiver Kendall Wright said when asked about his rookie quarterback. "We had plenty of opportunities to win that game before the last minutes."

Vikings players praised Keenum, who completed 17 of 21 passes for 140 yards and a touchdown. He replaced veteran Sam Bradford, who was sacked four times and aggravated his injured knee during the first half.

"It's real tough for a quarterback to come into that situation and do what he did," Minnesota running back Jerick McKinnon said. "Everybody believes in him, and he showed why."

McKinnon also did his part to replace an injured teammate. He rushed for 95 yards and a touchdown and led the team with 51 receiving yards in the Vikings' first game without star rookie Dalvin Cook.

Keenum rejuvenated the Vikings' offense. He opened the second half with a 13-play, 75-yard drive that ended with a 13-yard touchdown pass to tight end Kyle Rudolph. The play extended the Vikings' lead to 10-2.

A fake punt pulled the Bears within 10-9. Punter Pat O'Donnell caught a long snap and calmly lobbed a pass to Benny Cunningham, who spun off a tackle and raced 38 yards to the end zone.

"Great throw," Cunningham said. "He was patient. Throughout the week, we talked, missed it a couple times, did some extra reps yesterday. ... Just trusted him to make the right throw."

Minnesota made it 17-9 on a 58-yard touchdown run by McKinnon late in the third quarter. The diminutive running back burst through the right side of the offensive line for his first touchdown of the season.

Chicago evened the score at 17 on a touchdown and a two-point conversion with 12:24 to go in the fourth quarter. Trubisky spotted tight end Zach Miller in the end zone and fired a 20-yard pass that deflected off the outstretched hand of Vikings safety Andrew Sendejo and landed in Miller's hands.

Moments later, Trubisky ran for a two-point conversion on a trick play that fooled the Vikings' defense.

"I thought he was really good," Miller said. "He extended plays for us, made plays downfield, made plays with his legs. He put us in position to win that game."

The Bears' defense recorded a safety to open the scoring with 1:31 remaining in the first quarter. Defensive end Leonard Floyd sacked Bradford in the end zone to give Chicago a 2-0 advantage.

Minnesota grabbed a 3-2 lead on a 26-yard field goal by Forbath with 1:02 remaining in the first half. Vikings defensive end Everson Griffen set up the score with a strip-sack in the red zone.

The Vikings outgained the Bears 300-274 and won the takeaway battle 2-0.

"Our defense played extremely well," Keenum said. "I think they won the game for us there at the end. It was a great team win overall, but the defense played incredible all night."

NOTES: Bears QB Mike Glennon maintained his role as a team captain despite being benched in favor of rookie QB Mitchell Trubisky. ... Vikings RB Latavius Murray earned his first start of the season in place of RB Dalvin Cook, who is out for the season with a torn ACL. ... Bears LB Danny Trevathan served a one-game suspension for a helmet-to-helmet hit on Green Bay Packers WR Davante Adams in Week 4. ... Vikings WR Michael Floyd was activated to the 53-man roster and made his season debut after serving a four-game suspension for violating the NFL's substance-abuse policy. He made one catch for 19 yards. ... Bears LB John Timu injured his knee in the second half and did not return.