Smith, who has found starts hard to come by this term, replaced the suspended Shane Sutton who served a one-match ban in the 4-1 win over the Brakes.
Cowan insists ex-Shrewsbury man Smith took his chance with both hands and now poses the Bucks chief a selection problem for the New Year’s Day clash with Nuneaton.
He said: “Dom was immense, he was different class.
“I think I can say he has been patient, because he had a difficult start to the season when he was suspended for the first three games.
“Then there has been the quality of performances of the other lads who have come in.
“But he came in and took his chance and I am really pleased for him.
“It does pose me a selection headche.
“With Dom, you can’t be more appreciative or speak highly enough of the lad.
“His attitude and the way he is, it’s different class.
“He is one of those who puts his heart on the pitch, and he has been immense around the rest of the lads. There has been no sulking or moments when he has put his head down, he has waited for his chance and taken it so Nuneaton will be a tough one.”
That was the only change against Leamington as Cowan again left out James McQuilkin, Henry Cowans and Steph Morley, three of the top performers for the Bucks over recent months.
Cowan said that is the luxury he now has as Bucks boss, which isn’t something all other managers can enjoy.
He added: “Just look how lucky I am?
“I am fortunate to be able to bring on the lads I did, and they are first-team regulars.
“It is the difference from other teams, we are fortunate enough to have that strength in depth now.”