United took the lead in the 11th minute when Graham Westley rifled an angled drive past Royalists keeper Nigel Wiscombe for his 7th goal for the club.
Windsor equalised just 3 minutes when ex Duck Rowan Dodds outjumped Simon Mason to head a cross past Ducks keeper Paul O'Reilly.
Then in the 20th minute the hosts went 2-1 up in controversial circumstances when O'Reilly raced out of his area to intercept a through ball but his attempted clearance hit Windsor's Michael Creighton who sidefooted towards goal, O'Reilly rushed to get back to save at his near post but the linesman on the far side signalled that the ball had crossed the line and referee Mr Fish awarded a goal.
United's strong protests were to no avail and the official showed the red card to Ducks defender Phil Stacey for dissent.
Just 4 minutes later the visitors were level at 2-2 when O'Reilly raced to clear upfield, Westley sparang the offside trap and advanced into the box before slotting beyond the despairing dive of keeper Wiscombe.
Then in the 75th minute Westley crossed low for Andy Robinson to fire past Wiscombe for his 6th of the season to win it for United and send them up one place to 10th in the table.
David Figg