Referee Grant Hegley handed Boston two dodgy spot-kicks - plus one for the home side - but turned down three strong appeals from Barnet in the second-half as tempers started to flare. But sub Grazioli popped up in injury time to claim a deserved point for the Bees.
Ahead of kick-off Boston's defensive injury problems continued, but Paul Ellender did return from suspension to come in at centre-back.
Pilgrims manager Steve Evans clearly came with a plan as he sent out a solid five-man midfield and just Anthony Elding up front. And it worked a treat early on as Barnet were increasingly frustrated as they tried to build attacks from deep.
The first chance actually fell to the visitors as David Galbraith's chipped free-kick from 20 yards went just wide of the top corner.
It was obviously just a sighter as four minutes later he found the target from another set-piece 10 yards further back, dipping his shot over the wall and past the slow-to-react Lee Harrison in the Barnet goal.
The lead didn't last long, though, as the Bees grabbed an equaliser on the half-hour with their first meaningful shot. Jason Puncheon did well down the right and Magno Vieira simply could not miss as the cross found him unmarked inside the six-yard box.
Barnet should have gone ahead five minutes later when another forceful Puncheon run drew a foul by Jamie Clarke and ref Grant Hegley pointed to the spot. However, Ian Hendon's effort lacked finesse and Boston keeper Andy Marriott didn't have to do much to save the low shot with his legs.
That penalty decision was probably correct, but there was plenty of controversy about the one Hegley made in favour of Boston just before the break. With the ball disappearing harmlessly out of play, he ruled that Adam Gross had tugged back Francis Green in the box - and even though Tim Ryan's spot-kick was also straight down the middle it was enough to put the Pilgrims back in front.
Barnet piled forward after the break and it was no real surprise they grabbed an equaliser, with the impressive Puncheon again the provider. Again his cross fell to Vieira and this time he only had to put the ball in from three yards to bring the Bees level.
But the home fans were incensed they were denied three more penalties after the break as Kandol and Vieira appeared to be hauled down in the box before Ellender handballed in a hashed attempt at an overhead clearance.
As if that wasn't bad enough, ref Hegley then decided Ian Hendon's 84th minute handball was inside the box and Ryan stepped up to blast in.
Barnet refused to give up however, and Grazioli was on hand to turn the ball into the net from six yards on the turn after Hendon's knock-down.