The Pilgrims were resolute throughout and squandered the game's best three chances which fell to Kaine Felix, Mark Jones and Dayle Southwell.
Chorley applied plenty of late pressure but the Pilgrims held firm to claim a valuable draw ahead of Saturday's second instalment of the play-off drama.
United boss Dennis Greene had recalled his first choice stars after several were rested for Saturday's final day clash against Leamington and the Pilgrims made a purposeful start in the delayed 8.00pm kick-off due to traffic problems.
Chorley's Harry Winter cleared Max Stryjek's crossbar early on but the Pilgrims should have taken the lead when Felix latched on to a long ball over the top to cut in on goal but dragged his shot wide of the far post.
There was a let-off for Boston with Stryjek completely miskicking outside his box but James Dean was uable to divert the loose ball home.
United remained positive on the attack and Southwell's drive was blocked by keeper Sam Ashton while Jones' drive was deflected behind by Andy Teague.
The Pilgrims carved out a terrific chance seven minutes after the break when Felix skipped away down the right to supply a brilliant cross but Jones skied his six-yard effort over the bar.
The half was a battle throughout but United thought they had secured victory when Southwell met Zak Mills' 83rd minute free-kick but fired his close-range effort wide.
Chorley (4-2-3-1): Sam Ashton; Mark Ross, Andy Teague, Chris Doyle, Paul Jarvis; Adam Roscoe, Dale Whitham; Josh Hine, Harry Winter (Jake Cottrell 67), Jack Dorney (Chris Almond 78); James Dean. Subs (not used): Aaron Burns, Matt Flynn, Adam Mather.
Boston (4-4-2): Max Stryjek; Liam Marrs, Zak Mills, Carl Piergianni, Rene Steer (Kyle Dixon 77); Kaine Felix, Scott Garner, Grant Roberts, Nicky Walker; Dayle Southwell (Jake Hall 84), Mark Jones. Subs (not used): Marc Newsham, Jamie McGhee, Sam Vince (gk).
Referee: Kevin Mulraine.
Attendance: 2,022.
PIC: David Shipman.