The 21-year-old striker enjoyed a fine start to the season at The Hawthorns, scoring eight goals in his first 11 appearances across all competitions.
However, Berahino has endured a lean spell in front of goal recently and has failed to hit the target since a 2-2 draw with Crystal Palace on October 25.
Subsequently, head coach Irvine decided to leave him out of his starting XI for last weekend's 0-0 draw at Hull City and Saturday's 1-0 win over local rivals Aston Villa.
Irvine stated that he took the decision in order to protect the youngster from the limelight, but he has been pleased with Berahino's reaction and is convinced he still has a big role to play this season.
"He's certainly been training very well and has responded in exactly the way that you'd want to for a player who has been left out of the squad," he said.
"He'll be a really important player for us this season, there's no doubt about that.
"I think everybody realised Saido had been finding things a bit difficult, his performances hadn't been at the same level that he'd been showing earlier in the season.
"That was understandable because he's young player who we're asking a lot of, a lot more than anybody anticipated at the start of the season.
"I felt it was time to take a bit of the pressure off him, time to give him the chance to play with a bit more freedom and not feel as if everybody was looking at him all the time.
"I felt it was the right decision this week and last week. I was fairly certain I'd be using him at some point in the game, the big question was when and how.
"Funnily enough when I did bring him on it was during a period that we were on the front foot quite a bit. Saido came on and straight away was involved in the goal.
"At that stage we had four forwards on the pitch and I think they were all involved in the build-up to the goal."
