The Post's Jason Reid says after last night's loss to the Broncos, the Redskins need a win against the Chargers on Sunday if they want to do well this season. (Sarah Parnass/The Washington Post)

For a brief moment in the second half of their game against the Denver Broncos , it appeared the Washington Redskins had a chance to give Mike Shanahan a triumphant return to the city where he won back-to-back Super Bowls 15 seasons ago.

Takeaways by the defense on consecutive stands led to two quick touchdowns and a 14-point lead with just more than 11 minutes left in the third quarter.

But then Peyton Manning and the Broncos stormed back with 38 unanswered points in the final 23 minutes and defeated the Redskins, 45-21, on Sunday at Sports Authority Field at Mile High.

The Redskins (2-5) entered the game in need of a monumental performance from their defense and a highly effective offensive showing as they faced off with Manning and his league-leading attack.

Instead, Washington’s defense collapsed midway through the second half after a strong first 21 / 2 quarters. Meanwhile, Robert Griffin III and the offense did not have their best day. Griffin completed only 15 of 30 passes for 132 yards, a touchdown and two interceptions. He fumbled once and left the game with 5:53 to play after injuring his left knee while getting driven to the ground during his second interception. Kirk Cousins took over for the final stretch but threw two interceptions — including one that Dominique Rodgers-Cromartie returned 75 yards for a touchdown.

“It was ike a blur, ya know?” cornerback DeAngelo Hall said. “To be brutally honest, I don’t remember. I looked up one point, 21-7, felt good. Everybody’s smiling. Turned around and all of a sudden it was 38-21. I don’t really know what went wrong.”

Hall and his teammates felt good early in the third quarter because of two touchdown-producing turnovers.

On the fifth play of the third quarter, the pocket collapsed around Manning, and left outside linebacker Ryan Kerrigan knocked the ball from the quarterback’s cocked-back hand. Right outside linebacker Brian Orakpo pounced on the bouncing ball, recovering it at the Denver 19.

Washington’s offense took over and fed Morris on three straight plays — runs of four, 14 and one yard for the touchdown that put his team up 14-7. And two plays later, Hall intercepted a Manning pass intended for wide receiver Demaryius Thomas, who fell down. Hall returned the pass 26 yards for a touchdown.

It marked Hall’s third touchdown of the season (he has two on interception returns and one on a fumble return).

But the play didn’t rattle the Broncos (7-1). Stringing together an 11-play, 75-yard scoring drive capped by a four-yard Montee Ball run, Denver ended its drought and closed the gap to 21-14 with 7:48 left in the third quarter.

“I felt like that drive was crucial,” said Manning, who completed 30 of 44 passes for 354 yards and used four touchdown passes to overcome three interceptions. “We were down 21-7. We put our defense in a really tough spot with two turnovers back-to-back. . . . We gave them an easy 14 points there. I thought it was critical to answer.”

That first touchdown set off a scoring frenzy. Manning led four more scoring drives — touchdown passes of 1, 35 and 35 yards to Joel Dreessen, Knowshon Moreno and Demaryius Thomas, respectively, and a 19-yard field goal — to give Denver a 38-21 lead.

Washington’s offense went the other direction. Five of the Redskins’ final six possessions ended with turnovers.

Linebacker Von Miller sacked Griffin and forced him to fumble at his own 24, and Denver recovered. The Redskins’ next possession ended with a punt, but Washington got the ball back quickly when Manning was intercepted by safety Jordan Pugh. But just two plays later, Griffin threw an interception.

On the next possession, Griffin got hit hard as he unleashed a pass that was intercepted by Rahim Moore. As Denver defensive tackle Terrance Knighton drove the quarterback to the ground, Griffin hurt his left knee. He was checked on the sideline and shortly after got up and walked around but didn’t reenter the game.

Cousins relieved Griffin but threw two interceptions to seal the defeat.

“I was just disappointed,” Shanahan said. “We were up 21-7. All we had to do was get a couple drives offensively going, keep Denver off the field, and we could have dictated the outcome of the game. But a credit to them. They found a way to get us off the field, and they kept a couple drives going — third and fourth downs, making plays, and you can’t win football games when you have five turnovers in the game.”

The scoring flurry of the second half contrasted greatly from the first half, in which Washington and Denver mustered only seven points apiece. The Broncos got on the board first with a six-yard pass from Manning to Wes Welker but then had to punt on their next three possessions. Washington, meanwhile, punted to end their first four series and capped the half with a 16-play, 95-yard drive that ended with a seven-yard touchdown pass from Griffin to Leonard Hankerson to force a 7-7 tie at halftime.