There was no stopping promotion-chasing Hull after such a great start. With Walsall looking shell-shocked Hull piled on the pressure.
Stuart Elliott cracked in the second after 34 minutes with goalkeeper Joe Murphy and his defenders leaving it to one another and no-one attempting to stop the shot.
Junior Lewis almost increased Hull's lead when his header from a Green free-kick struck the foot of the post. But Lewis did not have to wait long when he powered into the area after 39 minutes and scored from close range.
Hull could not maintain the same pace and they were suddenly in a battle after Michael Standing put Walsall back in the game from 25 yards after 49 minutes.
With Paul Merson pulling the strings, Walsall dominated the rest of the match, but chances were missed and Merson admitted to being one of the guilty parties.
Hull should have made the game safe on the hour mark when Barmby found Danny Allsopp but the Australian striker slid the ball wide of the post.
It was a brief interruption to Walsall's pressure. Merson almost scored with a long range drive into the side netting and his team refused to give up in a display that he said was outstanding.