The hosts had won just one of their previous seven games but goals from Dave Edwards and Lee Evans breathed fresh life into their bid to make an instant return to the Championship.
Edwards, who had seen an earlier effort cleared off the line by Jack King, finally made Wolves' pressure pay in the 28th minute when he picked up a neat pass from Kevin McDonald and powered a shot past goalkeeper Declan Rudd at his near post.
Preston, who hit the crossbar through a Joe Garner cross three minutes after Edwards struck, had their fate sealed by Evans after 55 minutes when he made no mistake from close range after Rudd had pushed out a shot from James Henry.
Preston had arrived at Molineux on the back of five wins in seven league games and with three in succession. It was their first defeat in nine away league games.
Grayson said: "When you looked at the Wolves performance they had a lot of energy about them and some good quality. They should be putting on performances like that with the squad that they have got.
"I thought that we competed well with them. It was a close game and some decisions didn't go for us.
"Ian Hume's goal that was disallowed for offside must have been a really close call. We also had a good shout for a couple of penalties.
"You sometimes have to give the opposition credit but there were still positives to come out of our performance as well.
"If we had got the first goal then the place here can be a bit nervous. But we didn't and they were a vibrant team and we knew how they were going to play.
"We were probably just off it a little bit. Our decision making probably wasn't as good as it should have been.
"You look in the last 10 or 15 minutes of the game and we still play nice football but it has to go in the box. You have to test their back four.
"We have to learn from the lesson today but there were some decent performances. But you have to give credit to Wolves. They have international players, two years ago Premiership players.
"So credit to the opposition but we just felt that our decision making was taking too many touches, too many passes.
"It was nice football at times but sometimes you have to get the opposition turned and facing their own goal and that is what they did to us at times.
"We didn't do that enough to them. We were a bit too predictable. But we will learn from this game."