Cahill said: "If we had scored a second goal, it's over.
"We did control the game for long periods, but we just needed that second.
"If you score a second it's game over but the last 15 minutes it really opened up and they scored. It was one of those games.
"West Brom pushed three up front, then something can happen - a cross, a header and you get a point. That's what happened."