"I didn't expect it to go in," he said.
Duncan's goal in the first three minutes of the second half Thursday sparked top-seeded Jackson's 3-0 win over second-seeded Northwest for the Class 3 District 1 tournament title.
The Indians (16-5) added two goals in the final five minutes to capture their third consecutive district championship.
"Senior year, you can't ask for anything more," Jackson senior defender Dylan Blaylock said.
(Jackson players celebrate their 3-0 victory over Northwest during the Class 3 District 1 title game Thursday at Central High School.)
"To win 3-0, it's a great way to go into the sectional," Blaylock said.
Duncan, a senior forward, found himself all alone with the ball in the deep right corner near the flag early in the second half.
Duncan didn't have much of an angle as his shot headed toward the near post. It looked like Northwest senior keeper Andrew Hughes would make a routine save.
But Hughes mishandled the shot. The ball bounced off his hands and deflected off the post into the net just 2 minutes, 34 seconds into the final period.
Duncan's goal seemed to ignite the Indians, who dominated the second half while playing with a strong wind on the chilly, wet night at Central High School's new stadium.
"It really got our intensity up," Duncan said about the game's first goal.
The Indians possessed the ball on Northwest's end of the field for most of the final 40 minutes. They missed at least five dangerous opportunities, including several nice saves by Hughes, before finally breaking open things late.
Junior forward Keagan Cavanah's impressive individual effort made it 2-0 with 4:42 remaining. He dribbled around two defenders and blasted a shot past Hughes.
"That was a really nice goal," Jackson coach Zack Walton said.
Senior midfielder Clayton Baker, known for his long throw-ins, used his specialty to round out the scoring with 2:15 left.
Baker's throw-in from about 35 yards along the left sideline bounced high in front of the goal. Hughes mishandled the ball, it got by him and trickled into the net.
While Jackson's offense produced three goals, the Indians' defense was just as responsible for the win.
Jackson's back line of Blaylock, senior Zack Taylor, junior Austin Gammon and freshman Preston Arnold never let the Lions (16-12) sniff a prime chance.
And senior keeper Austin Baker handled himself well in the nets.
"You have to give our defense a lot of credit," Walton said.
Walton had special praise for Blaylock, who was given the assignment of marking Northwest star junior forward Gino Bono, who has 20 goals this season.
"Dylan did a great job," Walton said. "He shut Bono down, and he's a really good player."
Blaylock said he knew what to expect from Bono after the teams met earlier in the season. Jackson won that contest in overtime.
"We knew he was all they go to," Blaylock said. "I just did my best and he pretty much didn't touch the ball.
"Our defense just played really well, given the conditions. It's slick out there."
The squads battled through a relatively even first half. Jackson had a goal wiped out by an offsides call in the opening 13 minutes, but the flag came early and there were no objections.
Jackson then used the wind to its advantage in the final period.
"The wind made a big difference," Walton said. "I thought our defense did well in the first half. I didn't realize how well until we had the wind in the second half. It really made a difference."