Wolves Under 23s ran out 2-1 winners through goals from Donovan Wilson and Nouha Dicko before Joao Morelli netted a consolation for the visitors.
The result moved Wolves up to third in the PL2 Division 2 table after five games.
Speaking after Monday's game, Sellars said: “Since I’ve been here that was probably the best performance in terms of a 90-minute game.
“It was really focused, really concentrated, we showed moments of really good football and good intensity.
“So all the things we’ve been looking at and working at.
“We were able to dominate a really good Middlesbrough team who haven’t lost a game yet.
“From that point of view it was really encouraging and positive in terms of every game we’ve had this season. We’re maintaining our standards."
The Under 23s Coach explained that the current group of players has been together for a number of years and that is evident in their performances.
“Compared to last year, not much has changed in how the team’s playing but the way the team picks up results has changed, there are more goals in them.
“This team’s been together for three years and the majority of the group are 18-years-old, having played together in the youth team for two or three years.
“They’ve been coached well through the years by Rob Edwards and Jerry Gill.
“The methods are the same, we’re very consistent in what we do so when they come to me they don’t have to start again.
“The seeds that we’ve been planting over the last few years are really starting to come through and the players are really starting to prosper.
“There is a real team mentality about them. They’ve been successful in those three years and they’re bringing that mentality with them.
“They like winning, they enjoy working together, they enjoy training so all the good things that you’re looking for.
“All the good teams I have ever seen have that and it’s there in abundance with this team. They’re a joy to work with.
“The other groups perhaps didn’t have the quality, they didn’t have the goalscoring despite dominating games."
With a larger number of players in the first team, Scott Sellars has found that he has a more consistent group to work with on a daily basis.
And the Under 23s Coach believes this has helped when preparing his side for games.
“Walter has a bigger group and he likes to work with a bigger group," he said.
“That’s not being supplemented by young players so I’ve got a very sustainable group every day.
“We can work very much together, I know who I’m working with the day before.
“Because numbers last year were low, sometimes we could train the day before a game without the squad that we would be using for the game, and that can make messages more difficult.
“From my point of view it’s made my job a lot easier."
