Villa led twice through Ollie Watkins and a Diogo Dalot own goal in a thrilling second half that followed a desperate first.

But they had no answer to Garnacho's direct running as the Argentina wide-man became the youngest United player to claim two assists in a game as he created goals for Bruno Fernandes and then Scott McTominay, with a brilliant long pass into the heart of the visitors' box.

That positive contribution is in stark contrast to his experience on United's pre-season tour of Thailand and Australia, when he was prevented from playing in matches as a disciplinary measure after twice turning up late for team meetings.

And, while Ten Hag praised Garnacho for his performance against Villa, the Dutchman's words came with a clear warning.

"It depends on his approach, on his attitude," said Ten Hag. "If he keeps his attitude and wants to improve every day and when he is doing the right things in his lifestyle, it is possible.

"You can see he has capabilities and can contribute to attacking football. Also he has something, he can break open a compact defending line.

"All teams that want to attack, that want to play in opponents' half, they need players like that. He can outplay them and also in the final decisions he can do the right things."

Garnacho the star on frantic night at Old Trafford

Alejandro Garnacho replaced Anthony Martial with 28 minutes to go

The difference between the first half and the second could not have been more pronounced.

While the highlights of a tepid opening period were a needless yellow card for a clumsy tackle by Harry Maguire on Ollie Watkins and two speculative set-pieces by Douglas Luiz and Fernandes, the action after the break was electric.

It took Villa just three minutes to take the lead as Watkins finished superbly past Martin Dubravka after being sent clear by Jacob Ramsey.

The smoke from a flare set off in celebration of Villa's opener had not even begun to clear by the time Fernandes crossed for Anthony Martial to equalise a minute later.

When Dalot turned Leon Bailey's header into his own net, new Villa boss Unai Emery must have thought he was going to start his reign with successive victories.

He reckoned without Garnacho. The youngster was involved in the equaliser as Ashley Young stretched to prevent him getting to the ball and inadvertently set up Rashford, who steadied himself before applying a fine finish.

The best was yet to come, though.

It seems such a daunting comparison, but those who were there when Cristiano Ronaldo took Bolton apart on the same wing, in the same area of the field 19 years ago, could not escape the feeling they were watching something similar again.

That the pair should now be team-mates seems bizarre.

But, as Ronaldo's influence is without question beginning to wane, Garnacho's career is all in front of him.