With the Baggies trailing 2-0 at the break, Anichebe came off the bench to halve the deficit on 51 minutes before winning a last-gasp penalty that Saido Berahino converted to salvage a draw.
"There's no doubt he [Anichebe] made a difference and I thought before the game that we might need him," Irvine told reporters.
"Having watched Palace and looked at their strengths and the way they're able to play then I felt as if Victor would be needed at some point during the game.
"Unfortunately he wasn't quite ready to start the game but it was important he was fresh enough to make an impact if we needed him. He came on earlier than I planned but it was a case of needs must."