Mantom was then given his marching orders late on for a high challenge on Joe Garner.
Grayson said: "We had a poor period just after we got the goal, but to be fair to Walsall you know what you're going to get from them.
"We didn't talk to each other enough but the players grasped it and we had some good opportunities in the second half, their 'keeper made some real good saves from our front two, who were a threat.
"It would have been a huge disappointment if we'd not won the game but we have and that's all that matters at this stage of the season."
On the red card, Grayson admitted luck might just have been on their side this time at Deepdale.
"The ball's just bounced and Joe's got it away," he added.
"The lad's probably caught him halfway up his shin. I've seen them given as red. I've seen them given as yellow.
"We've had decisions with yellow and red cards go against us so you're not going to complain too much."
- Sports & Recreation
- Paul Downing
- Bailey Wright
- Sam Mantom