The 5-0 triumph at Deepdale, North End’s biggest of the season, moved them within five points of the play-offs with a trip to Leeds next up on Saturday.
Tom Barkhuizen got things going in the 25th minute with his sixth in six games but it was four goals in 21 second-half minutes that put the relegation threatened Robins to the sword.
Aiden McGeady scored from the penalty spot before a Tom Clarke header made it three and Callum Robinson’s brace completed the rout.
“It’s a great result for the supporters and everybody,” said Grayson.
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“The players are confident and I think this is only going to increase the confidence level.
“We’re straight back in to prepare for another tough game at the weekend and we’ll try and build on this.
“Some of the goals we scored, some of the play we had was exceptional.
“The players are enjoying what they’re doing and it was a great night for us.”
There was no indication of what was to come at the interval but the struggling Robins never recovered from the moment Robinson was brought down for the penalty just 28 seconds into the second half.
“The words we used at half-time were that we were okay without being spectacular or as good as we could be,” said Grayson.
“The second goal was a big one straight after half-time and scoring the third one so quickly gave the players the opportunity to go and build off that.
“If you can’t enjoy yourself at three or four nil then you’re never going to be able to.”
On a night where several players stood out it was McGeady who took man of the match honours on his 31st birthday.
“He’s enjoying what he’s doing and some of the movement of his feet is frightening at times,” said Grayson.
“He can be unplayable and I do feel sorry for Championship defenders.
“He should be playing in the Premier League but let’s hope he’s with us next year doing his stuff.”
It was a miserable night for Bailey Wright though, the Australian receiving a mixed reception as his new side, one point above the bottom three, were well beaten on his Deepdale return.
“The only thing was I was a little disappointed with the fans’ reaction to Bailey during the game,” Grayson said.
“He’s been a good servant for the club and players come and go and managers come and go.
“I’m not having a go at the supporters I’m just a little bit disappointed we didn’t show him the respect he deserved.”