Twenty unanswered points to begin the second half would prove to be the difference as Rosepine fell in its first game of the year.
Mangham scored three touchdowns in a four-minute span to pick up the 34-26 win Friday night at McKee-McCain Stadium.
Despite the loss, head coach Brad Ducote was happy with the way his guys responded to a big deficit.
"I learned there was no quit in them," he said. "They played four quarters, start to finish. We had a few things not go our way and a few mistakes. They could have easily folded tent, and they fought right back to stay in the game."
The Eagles got on the board first with an 8-yard touchdown pass from Ethan Frey to Josh Cummings.
Frey threw for three touchdowns and 158 yards in his debut behind center.
"I thought he did an excellent job in his first start," Ducote said. "Of course, we, as a coaching staff, have high expectations for the young man. He played well and we only look for him to get better."
Trailing 14-7 in the second quarter, Braden Nolen got free for a 7-yard touchdown to tie it at 14 heading into halftime.
In the third quarter, Mangham scored on a 3-yard run and on a 5-yard run just five seconds later after a miscue on a kickoff return.
"That put them up several scores, and I said 'let's see what we are made of,'" Ducote said. "It could go one-of-two ways: we can fight back and get back in the game or we can lay down and give up 50. We fought back. I was super proud."
With 7:12 to play, the Dragons connected on a 26-yard touchdown pass to go up 34-20.
Frey hit Cole Donahue for two touchdowns in the fourth, but it was too late as the Eagles fall to 0-1 on the year.
"Mangham played a tough schedule last year, and when I looked at them on the film, I knew they were going to give us problems," Ducote said. "I don't know if they fully understood or took it for granted. It was kind of humbling for them and for me, as well. It was a good game for us, regardless. Even though it was a loss, I walked out it with a positive attitude and still a lot of excitement for us."
Rosepine takes on South Beauregard on the road next week.