Briers had given the Pilgrims an 18th minute lead, but the Stags levelled proceedings up 11 minutes into the second period.
With a revamped line-up ahead of their impending FA Youth Cup clash against Burnley, United were missing five players from the outset who are likely to start against the Clarets.
The reshuffle afforded Scott Langan and Todd Devlin the opportunities to impress in the full-back positions, while under-19s striker Tom James partnered captain James Tricks in attack.
A fine move down the United right brought the Pilgrims’ breakthrough, with BRIERS arriving to drive a rising effort high into the top corner from 20 yards.
Mansfield equalised on 56 minutes through Blake VINCENT — and that is how the scoreline remained.
Boston (4-4-2): Marc Hipwell; Scott Langan, Lewis Sturman, Jordan Lote (Jordan Nuttell 60), Todd Devlin (Niall Delahoy 65); Jake Platten (Charley Sanders 68), James Reed, Jake Beauchamp, Joe Briers; James Tricks, Tom James.