The Pilgrims led at Curzon Ashton through Finley Thorndike's first goal for the club, but lost Nixon after referee James Bancroft adjudged that he had made no attempt in playing the ball when fouling Tom Peers, who subsequently drew the Nash level from the spot.
Billy Chadwick re-asserted United's lead from the penalty spot before half-time - but Ryan Hall's last-gasp leveller denied Boston all three points, albeit with the Pilgrims securing their safety in National League North regardless.
Manager Ian Culverhouse had made three changes ahead of kick-off, with fit-again Ethan Sephton restored at full-back, and starts for Thorndike and Wright.
The Pilgrims took the lead in the 31st minute, with a fine move originating from Cameron Gregory and involving Zak Mills, Chadwick and Wright before THORNDIKE slammed home from inside the penalty area for his first goal in United colours.
Curzon responded and referee Bancroft penalised Nixon for pulling Peers' shirt as they jostled to meet Craig Mahon's cross from the right. Bancroft deemed that Nixon had made no attempt to play the ball, despite PEERS having hold of his opponent too, and the Curzon man blasted home the subsequent spot-kick.
United responded positively and won their own penalty with Wright wiped out by Devon Matthews, who was not handed a card after being deemed to make a genuine attempt on the ball. CHADWICK crashed the ball home from 12 yards to give the 10 men something to defend after the break.
The Pilgrims battled manfully in the second period against their play-off chasing hosts and came close to shutting Curzon out altogether. Gregory made one fine save with his legs to deny George Waring, while substitute Jo Cummings produced a terrific block to deny Dylan Boyle.
The Nash finally levelled on the stroke of full-time when a ball was poked in behind the United rearguard and HALL stabbed home to earn Adam Lakeland's side a point ahead of their final two fixtures against title chasers AFC Fylde and King's Lynn Town.
Curzon (3-5-2): Chris Renshaw; Marcus Poscha, George Waring, Devon Matthews; Craig Mahon (Jordan Richards 73), Will Hayhurst (Ryan Hall 59), Adam Barton, Dylan Boyle, Finlay Armstrong; Jimmy Spencer, Tom Peers (Josh Hancock 73). Sub (not used): Dillon Edmundson.
Boston (4-1-2-1-2): Cameron Gregory; Tom Nixon, Luke Shiels (Jo Cummings 70), Ben Pollock, Ethan Sephton; Tom Platt; Zak Mills, Will Atkinson; Finley Thorndike; Jake Wright (Jordan Burrow 75), Billy Chadwick (Keenan Ferguson 79). Subs (not used): Tre Mitford, Sam McLintock.
Referee: James Bancroft.
Attendance: 555.
PIC: Chris Bray.