A poor defensive display led to Boro being dumped out of the FA Trophy at the first hurdle.
In the opening stages they looked threatening, with Will Joseph and Dan Edwards going close.
At the other end, Ben Harris saved from Matt Weston and Craig Livingstone drove wide.
After 25 minutes, Jamel Carr found himself unmarked when he got on the end of a deep cross to convert from close in and put Casuals ahead.
Just nine minutes later Weston shot from distance to double the lead.
Boro replied immediately when Joseph smashed home a Jey Silva cross.
Just as half time approached a harmless looking cross from Sonny Farr, caught the wind and drifted over Harris and into the net for a third Walton goal.
Boro were given a lifeline when they were awarded a penalty after the ball had bounced up and struck a defender, Dan Edwards converting the spot kick.
With full time approaching, Boro searched for an equaliser and when Jerry Lyons got on the end of an Edwards cross they looked to have salvaged a draw. Instead it was Walton who had the final say when they went staright back from the kick off to win with a weak looking shot from John Ambridge,which crept under Harris.
BORO: Haris, Williams, Twagira, Glynne, Campbell, Kendall, Edwards, Warrell, Joseph, Flowerday, Silva. Subs Used: Body,Lyons.