The in-form striker scored the only goal of the game at the Riverside as Chelsea beat Middlesbrough 1-0.
Costa scored the only goal of the game at the Riverside, pouncing after a first-half corner rebounded inside the six-yard box, and now tops the Premier League goalscoring charts with 10 goals from 12 games.
Perhaps just as significantly, he has not been booked since the middle of September, and whereas post-match discussions would once focus on a perceived lack of discipline and a penchant for arguing with officials, it is now Costa's football that is doing the talking.
"Diego is always important, not only for today," said Conte. "He is our point of reference in attacking. He is impressive in the way he is finding his goals, and it is important to continue this way because we need his goals.
"Is he focused just on his football? It is important to have this question. In the past, people have been asking me about his behaviour and his reactions, but now as a striker, I think he is one of the best in the world.
"He has to continue this way, and he is showing his patience in the right way and is focused on helping the team, with and without the ball."
With Liverpool having failed to beat Southampton on Saturday, Chelsea's victory took them to the top of the table for the first time under Conte's management.
Having won their last six games without conceding a goal, they are one point clear of both Liverpool and Manchester City, although Conte feels it is far too early to be talking about their title-winning credentials.
"I think that now it is difficult to reply to this," he said. "Only a month and a half ago, you saw Chelsea conceded two defeats to Liverpool and Arsenal.
"After this, Chelsea were not a favourite or a team who could fight for the title until the end. Now, it is difficult to change that opinion completely.
"We are working well, but if you ask what is our target, I want to wait until the end of the first part of the championship.
"It's hard to say if we're the best side in the country right now, but I'm pleased with the players because they know our fans demand that we must fight until the end. I'm seeing with my own eyes that we have special players."
Things are about to get more difficult for the league leaders, with next weekend's home game with London rivals Tottenham Hotspur preceding a trip to Manchester City.
"We're ready to play many games in a few days because from the start of the season, we've worked not only on the tactical aspect but also the physical aspect," said Conte.
"You need the strength to run from the start to the end with good technique and talent. If you link the two, it's important.
"Our trust in what we're doing and how we are working is increasing, and now it's important to focus on the next game, a massive one against Tottenham."
Having claimed recent draws against Arsenal and City, Middlesbrough produced another spirited display against one of the title contenders. However, for all their improved form, Aitor Karanka's side are just one point clear of the relegation zone.
"Playing against a team like Chelsea, we knew it would be tough," said the Boro head coach.
"One mistake punished us, but we have shown we can compete against the best teams in the league. You can't be pleased to lose one game, but I am pleased with the attitude of the players."