Ormskirk-born Dowell's long-range effort put Everton 3-0 against the Saints with the eventual 3-1 victory lifting the young Toffees up to third in the table.
Brendan Galloway and Sam Byrne also on target as the young Toffees secured a fourth consecutive victory.
Speaking after the game Unsworth was full of praise for the youngster's vision, confidence and stunning technique:
"I was delighted to be on the right side of the pitch to witness Kieran’s goal because it’s one of the best goals I have ever seen.
"It was absolutely outstanding. He gave a great performance in a bit of a different role to what he has been playing recently and he showed some great touches just off the striker.
"That goal alone was worth coming to watch the game for. It was great execution. We see that sort of stuff in training every day and now he’s bringing it into the games and producing moments of magic like that consistently, which you have to do as a young player."
19-year-old Dowell has been at the club since the age of seven and signed his first professional contract with the club last March.
He has already made his senior debut, featuring as an early substitute against Krasnodar in the Europa League last season.