Foster's 67th-minute double save from Luis Suarez and Andy Carroll helped keep Kenny Dalglish's side at bay, before Peter Odemwingie stole all three points for the Baggies eight minutes later.
He told the WBA website: "The back four were like monsters, heading everything and kicking and clearing.
"They were absolutely amazing but to get that clean sheet as we did was absolutely phenomenal. The post got hit a few times, there were shots cleared off the line and even blocks from their players on our goalline.
"There was one shot that I thought was a goal. It hit the inside of my leg and I thought it was in the net, then I turned around and it was sitting right behind me.
"There was one that hit the bar and hit my back and still didn't go in, and the one that hit me in the face had the lads saying 'nice one Ben' - but I got nowhere near it!
"But we were absolutely buzzing afterwards."