The Pilgrims led through Richie Allen's own goal and Jay Rollins' strike at the break, with Michael Nottingham having initially equalised for the hosts.
United soon found themselves behind following goals from James Poole and John Johnston inside a six-minute period during the second half, but Smith's strike 10 minutes from time ensured parity.
The Pilgrims, deploying a five-man defence on their first-ever visit to Moor Lane, took the lead in the 10th minute when Lewis Hilliard’s deep free-kick was headed goalwards by Smith and inadvertently turned underneath his own crossbar by ALLEN.
United’s lead lasted only five minutes though, with Jordan Hulme glancing Sam Walker’s corner towards goal and NOTTINGHAM applying the finishing touch from close-range.
Chances remained at a premium, although home keeper Jay Lynch did make a routine save to deny Smith on the half-hour mark.
United inched in front again nine minutes before the break when ROLLINS broke through the offside trap before motoring clear and checking back to stroke the ball beyond Lynch’s reach and into the far corner.
Dion-Curtis Henry made a magnificent save eight minutes after the break to keep United in front, spreading well to thwart Allen who had galloped clear.
The home side gradually cranked up the pressure and Henry saved with his legs to deny Walker but Salford did level in the 67th minute when POOLE was allowed too much time before picking his spot after a quick throw-in had dissected the left-hand side of United’s defence.
Hulme was subsequently inches away from converting a JOHNSTON cross before the latter sailed home a low drive, via a wicked deflection off Jason St Juste, to hand the hosts the lead for the first time with 17 minutes to play.
United were undettered through and once substitute Waide Fairhurst had cracked the post following a well-worked free-kick routine, Marcus Marshall turned the ball back across goal for SMITH to nonchalantly backheel home the Pilgrims’ equaliser on 80 minutes.
Salford (4-4-2): Jay Lynch; Dominic Smalley, Michael Nottingham, Simon Grand, Stephen O’Halloran; Matt Warburton, Sam Walker, Richie Wellens (John Johnston 35), Richie Allen; James Poole (Josh Hine 83), Jordan Hulme (Mike Phenix 82). Subs (not used): Craig King, Bradley Barnes.
Boston (5-4-1): Dion-Curtis Henry; Kalern Thomas (Cameron Johnson 78), Joe Maguire, Marcus Marshall, Joe Robinson, Ben Gordon; Jay Rollins, Liam Agnew, Lewis Hilliard (Waide Fairhurst 78), Courtney Wildin (Jason St Juste 57); Gregg Smith. Subs (not used): Callum Chippendale, Lamin Colley.
Referee: Anthony Tankard.
Attendance: 1,425.