DENVER — In all those years roaming the sidelines in Denver, Mike Shanahan never saw one get so ugly, so fast.
Not surprisingly, Peyton Manning had a hand in turning Shanahan’s homecoming sour.
After being showered with applause, then staked to a two-touchdown lead, the Broncos’ old coach watched Manning and the Broncos score the last 38 points Sunday in a come-from-behind 45-21 victory over the Washington Redskins.
Manning overcame four turnovers and threw for 354 yards and four touchdowns, as the Broncos came back from a 21-7 deficit early in the third quarter. Manning hit the halfway point of the season with 2,919 yards — the most through eight games in NFL history.
‘‘You can’t give Peyton that many opportunities because he’s going to take advantage of it,’’ Shanahan said.
With Washington ahead by two touchdowns after Manning threw a pick-6 to DeAngelo Hall when receiver Demaryius Thomas fell on an out route, Shanahan squinted into the sunlight, rolled-up game plan in hand, and looked at a familiar sight on the scoreboard in Denver — his team comfortably ahead as the sun began to set over the Rockies.
Things changed quickly, though.
Manning led the Broncos (7-1) on a 75-yard scoring drive to make it 21-14, the key play coming when Knowshon Moreno ran for 5 yards on fourth and 2 from the Washington 22.
Then, after the defense forced a punt, it was Manning picking and poking again, moving Denver 83 yards in 16 plays for the tying score, a 1-yard pass to Joel Dreessen on the first play of the fourth quarter.
Robert Griffin III threw three straight incompletions and Sav Rocca followed by shanking a punt 15 yards. On the next play, Manning gave Denver a 28-21 lead with a screen pass Moreno took in for a 35-yard touchdown.
Von Miller ended the next drive with a sack and forced fumble to help Denver to a field goal, and Washington (2-5) never got closer.
‘‘It was like a blur,’’ Hall said. ‘‘Someone asked me, ‘What went wrong, what happened?’ To be brutally honest, I don’t remember. I looked up one point, 21-7, felt good, everybody smiling. Turned around and it . . . was 38-21.’’
The Broncos knocked Griffin out of the game late with an injured left knee, then got their final touchdown when Dominique Rodgers-Cromartie picked off backup Kirk Cousins and returned it 75 yards.
But all the video-game numbers — the franchise-record 31 fourth-quarter points, the 343 total points through eight games, most in league history — masked some growing problems for the Broncos.
Yes, Manning went 30 for 44 and hit four receivers for scores, including Wes Welker. But Manning also doubled his interception total and lost a fumble.
The Broncos forced five turnovers, including interceptions by Chris Harris, Rahim Moore, and Shaun Phillips.