The midfielder’s first-half brace was enough to comfortably secure the points, as Saints dominated large periods, and safeguarded their spot at the top of Group B.
The slick surface of Vicarage Road suited Radhi Jaïdi’s youngsters, who were able to put together smart passages of play, and impose their style on Watford.
“We imposed ourselves and played some very good football first half,” Jaïdi asserted. “We scored two early goals so that gave us a good footing in the game. That gave us the confidence, then second half was about managing the game.”
"There are a lot of positives, we created a lot of chances and could have scored more. I thought we dominated the game, and we imposed our style of football. We felt comfortable, not too challenged.
"I’ve been talking informally with Callum [Slattery], and insisting that he keeps his consistency. Keep sending the right messages every game, every training session, and any opportunity. Today sums it up, he’s taking things on board so he needs to keep that hard work.
“We bounced back from last week, we all knew last week’s result [against Cardiff] was a little accident, but we’re back to the top of the group now and we want to make the knockout phases.”
There were only five minutes on the clock when the 19-year-old midfielder’s free-kick was missed by everyone in the penalty area and crept into the bottom corner.
Slattery then converted a 33rd-minute penalty after Siph Mdlalose had been felled by Ben Jones.
Their third Group B victory takes Saints on to nine points, two clear of second-placed Blackburn Rovers, having played one match more.
Watford are bottom with four points from five matches.