Lescott arrived at The Hawthorns in June on a free transfer after his release by Manchester City but injury meant he missed the opening four matches of the season.
West Brom failed to win any of those games, but when Lescott made his debut at Tottenham they collected all three points in a 1-0 win.
Another three points followed on Sunday as Burnley were swept aside 4-0, with Lescott lining up alongside Craig Dawson for a second successive match.
And head coach Irvine cited the 32-year-old's experience as a vital component in West Brom's revival.
"His positional sense is very, very good and, as we know, if centre-backs stand in the right positions, they cut out a lot of the danger before it even comes," the Scot told talkSPORT.
"He has come in and has been a great influence on people around him.
"He has been a very, very important player to us, but he has been part of a great team performance in both the Tottenham and Burnley games."
Sunday's win lifted West Brom up to 10th in the table ahead of their trip to Anfield to face Liverpool on Saturday.
