The Black Cats looked on course to take a 1-0 lead into half time of their Premier League curtain raiser courtesy of Lee Cattermole's fifth-minute opener.
"It was soft a soft penalty for us. I've got to say I didn't look at the referee straight away for a penalty. But I was delighted that we got it," Irvine told BBC Sport.
"We came back from being an early goal down to a fantastic strike by Lee Cattermole. I'm pleased about that and about a lot of aspects of our performance.
"We're obviously still trying to get a number of our players up to speed."
Berahino bagged his second to fire the Baggies ahead on 74 minutes, but Sebastian Larsson pounced in the closing minutes of normal time to rescue a point for Sunderland.