And the Newcastle striker set up the winning goal for Tammy Abraham as England left it late to claim victory against China.
In the opening game of the Young Lions' Maurice Revello Toulon Tournament campaign, Middlesbrough defender Dael Fry had cancelled out Yan Dinghao’s first-half header.
And in the 89th minute, Armstrong centred for Abraham to net the winner. Both Armstrong and his United team-mate Freddie Woodman played the whole game.
Meanwhile, Adam Wilson started for England under-18s as they finished the Panda Cup with victory over Hungary under-19s on Sunday.
He played for the opening 45 minutes, having been an unused substitute in a 1-0 loss to hosts China under-19s on Friday. Winger Wilson appeared as a late substitute in their tournament opener, a 2-2 draw against Uruguay last Wednesday.