The Pilgrims were good value for their share of the spoils, with Gregory sustaining an ankle injury in the first half but playing on bravely.
He made a super save in the second half to deny Harrison Burke, while Jacob Hazel forced Wyll Stanway into a fine late stop as honours ended even.
Manager Ian Culverhouse had made three changes ahead of kick-off, with Ethan Septhon and Keziah Martin recalled, alongside a full debut for Sam Smart.
United could well have found themselves behind on two occasions early on - but home striker Owen Windsor lost his footing in both situations, the first of which after rounding Gregory.
Gregory played on after sustaining an innocuous-looking injury, despite being in significant discomfort, and he repelled a towering header from Burke on the hour mark.
United protected their goalkeeper with real authority, led by the dominant Michael Bostwick and Tom Leak, although Jordan Richards was well-positioned to divert another Burke header to safety off the line.
The Pilgrims had their own glorious chance late on when Hazel crashed goalwards from 20 yards - but Stanway stood firm - as United avoided defeat at the Deva Stadium for the first time against the 'new' club in Chester.
Chester (4-1-2-1-2): Wyll Stanway; Kieron Coates, Harrison Burke, Matty Williams, Joel Taylor; Kevin Roberts; Declan Weeks, George Glendon; Elliott Whitehouse; Christian Norton (Kole Hall 61), Owen Windsor (Reece Daly 76). Subs (not used): Tom Sparrow, Iwan Murray, Frankie Maguire.
Boston (4-3-3): Cameron Gregory; Zak Mills, Michael Bostwick, Tom Leak, Ethan Sephton (Brad Nicholson 45); Keaton Ward, Jordan Richards, Keziah Martin; Deji Sotona (Dylan Hill 81), Jacob Hazel, Sam Smart (Jimmy Knowles 65). Subs (not used): Michael Gyasi, Sam Essien.
Referee: Shaun Taylor.
Attendance: 1,957 (59 visitors).
PIC: Rick Matthews.