Broncos star cornerback back Pat Surtain II looked at the scoreboard in the fourth quarter and figured it was a lost cause.

The Broncos had trailed by 19 points to the New York Giants entering the quarter and were down by 18 with less than six minutes left. So of course it looked bleak Sunday at Empower Field at Mile High.

“I lost hope,’’ Surtain said after the game. “I ain’t going to lie. I lost hope.”

Nevertheless, “Don’t Stop Believing” was playing out of the loudspeakers late in the game. And the Broncos amazingly mounted a comeback after many in the crowd of 75,788 had long since headed for the exits.

The Broncos stormed back to stun the Giants 33-32 on a 39-yard field goal by Wil Lutz on the final play. It tied for the biggest fourth-quarter comeback in the 66-year history of the franchise and the 33 points scored in the fourth set a team record for most in any quarter.

“I don’t even know how to score 33 points in a quarter,’’ said Denver quarterback Bo Nix. “That’s kind of insane.”

The Broncos (5-2) won their fourth straight game and took over the AFC West lead, the first time they have been alone in that spot since Week 4 of 2016. They did it on Alumni Weekend in front of about 160 former players on a day that the 2015 Super Bowl 50 team celebrated a 10-year reunion and that late receiver Demaryius Thomas, a star on that team, was inducted into the Ring of Fame.

“I’m very thankful and very relieved to win a game like that,’’ Nix said. “It’s the best thing ever. My first time winning a game like that. We just kept making plays and kept the hope until the very end.”

As for Surtain, yes he did regain hope at one point in the fourth quarter. He said a key play in that happening was linebacker Justin Strnad intercepting a pass from Jaxson Dart and returning it to the Giants 19 with 4:47 left and the Broncos down 26-16. That led to Nix making it a one-possession game when he hit RJ Harvey with a 2-yard touchdown pass with 3:51 remaining to cut the deficit to 26-23.

“That probably was the difference in winning and losing the game,’’ Broncos coach Sean Payton said of Strnad’s pick.

The anxiety for Payton, though, was just getting underway. Minutes after talking about the interception, he took off his hat to show his hair.

“It keeps getting grayer,’’ he said.

Some of that graying no doubt happened in the waning moments. The Broncos took a 30-26 lead when Nix scored on an 18-yard run with 1:51 left.

The Giants (5-2) then mounted a last-ditch drive that culminated in Dart scoring on a 1-yard run to put the Giants up 32-30 with 37 seconds remaining. But Jude McAtamney botched the extra point, his second such miss of the game.

That 65-yard drive was helped by a roughing the passer call on Denver’s John Franklin-Myers and a controversial 38-yard pass interference call on Riley Moss that moved the ball to the 2. Payton then stormed onto the field to complain about the penalty and was flagged for unsportsmanlike conduct.

“I can’t criticize the officials but I can disagree with them,’’ said Payton, who acknowledged that going onto the field was “silly.”

But Nix and his teammates on offense soon made Payton feel a lot better. Taking over at their 23 with 33 seconds remaining, Nix threw a deep pass down the middle to Marvin Mims Jr. for 29 yards. Then he threw another deep ball to Courtland Sutton down the left side for 22 yards, setting the stage for Lutz’s winning kick.

“There’s no flinch,’’ Sutton said. “Until the clock says zero, we got a chance.”

Payton said Sutton’s catch came on a play that had just been put in Saturday. It was the last pass of the day for Nix, who completed 27 of 50 throws for 279 yards and two touchdowns. In the fourth quarter, Nix was 16 of 25 for 174 yards and ran for 46 of his 48 yards while scoring two touchdowns.

“What’s crazy is we installed (the pass to Sutton on Saturday) and the first live rep we got is what you just watched,’’ Nix said. “Courtland Sutton is just the man. That’s all I can say.”

Sutton caught six passes for 87 yards on a day in which he honored Thomas, who became his good friend when Sutton was a rookie in 2018. Sutton arrived at the stadium wearing a Thomas No. 88 jersey and donned it afterward at a news conference.

There was a logo near the field Sunday of Sutton’s No. 88. It was emotional at halftime when the 2015 team walked in wearing their game jerseys from that season and Sutton’s placard at the stadium was unveiled to officially place him in the Ring of Fame.

“It was an emotional day,’’ Sutton said. “I had to reel myself back in and not let my emotions take away from the focus that I needed. … It was emotional to see how many 88 jerseys there were out to support the Denver Broncos. … For us to get a win makes it that much more special. We didn’t want a dark cloud to be over something so special.”

There was a dark cloud over the Broncos for three quarters when they could generate little offense. They finally got on the board when Nix threw a 2-yard touchdown pass to Troy Franklin on a ball deflected by Sutton into his hands. Nix then tossed a 2-point conversion pass to Sutton to cut the deficit to 19-8 with 10:14 left in the game.

Dart followed that with a 41-yard touchdown throw to Theo Johnson with 10:14 remaining on a pass that bounced off the hands of receiver Wan’Dale Robinson. That gave the Giants a 26-8 lead.

That remained the score when the clock ticked under six minutes. According to NFL research, the last 1,602 teams trailing by 18 or more points in that position all lost. Since 1970, teams in that situation had been 1-3,677.

But the Broncos cut the deficit to 26-16 with 5:13 left on a 7-yard run by Nix and a Nix 2-point conversion pass to Franklin. Then Dart threw his pivotal interception.

“I can’t do that,’’ said Dart, who completed 15 of 33 passes for 283 yards and three touchdowns, two in the first half when the Giants took a 13-0 lead. “We were in full control of the game. That was an unacceptable mistake.”

After Lutz’s winning field goal, Giants coach Brian Daboll threw his headset down in disgust.

“They made some plays,’’ Daboll said. “Give them credit. We lost the game. It was upsetting.”

In the end, the Broncos were elated and relieved.

“It was a crazy back-and-forth game,’’ Payton said. “We had to find a way to clean up our mess.”

Payton said the Broncos must get a lot of things “cleaned up” from their sluggish first three quarters but he welcomed his players to celebrate until Monday.

They certainly were doing that in the locker room.

“Having the biggest comeback in Broncos history is huge and we’re so excited,’’ Mims said of the Broncos tying the record for the biggest fourth-quarter comeback first set in a 21-19 win over the Baltimore Colts in 1983.

“I’m never been down by that much and won,’’ said Denver outside linebacker Nik Bonitto. “It was crazy. I’m still geeked.”

And even though Surtain admitted he lost hope at one point, he said, “One thing we didn’t lose was our composure and we fought to the end.”

Surtain might not have been believing when “When Don’t Stop Believing” played, but that apparently did not last long.