Forest ran out 2-1 winners over high-flying Boro on Saturday, with Antonio playing a starring role in the fixture.
The rapid winger was a constant menace for Dougie Freedman's side and set up Forest's winning goal by powering past Kalas before squaring the ball to Dexter Blackstock.
It was a display which highlighted just how dangerous Antonio can be and Kalas admits he failed to get to grips with the former Sheffield Wednesday man.
“For the second I should have been quicker and stronger to win the ball or at least fouled Antonio. I didn’t do those things and then the goal happened," he said.
“We knew most of the balls would go to him and what type of player he is but we didn’t learn from what the coach had told us to expect."
Antonio has arguably been Forest's player of the season so far, with his performances consistently excellent throughout the campaign.
While many of the Reds players have suffered dips in form, Antonio has been a key outlet for the side and Forest's attacks are generally built around his talents.
Although Antonio isn't the most orthodox of wingers, his direct running and strength means that he poses a threat to every defender he faces and Middlesbrough clearly weren't able to deal with him.
That is testament to his ability, as Boro are one of hardest outfits to break down in the Championship, and Antonio will be hoping that he can sustain his excellent form for the remainder of the campaign and help Forest to mount a late top-six challenge.