Five minutes later it was 2-0 when Jason Roberts smashed home after Morten Gamst Pedersen had knocked on Paul Robinson's long kick.
Four minutes from time Roberts stabbed home a second from close range.
Allardyce said: "I didn't see that coming after half-time. We played very poorly for us at home in the first half and I had a bit of sorting out to do.
"At that stage it was all Newcastle and I was a little bit worried.
"But the one thing the players did was keep hold of their defensive qualities to make sure we stayed in the game.
"Psychologically it is very good. It means if we continue to win football matches we don't go down there anymore."