Celtic shaded the first half, but fell back to defend the draw in the second half and paid the penalty.
The opening was end to end. Almost from the kick off, Paul Bastock saved well when Craig Hobson put Phil Marsh one-on-one, but the Boston keeper stood up well. Almost immediately, Boston were attacking with Danny Sleath's distance effort crashed back off the post. Back at the other end and Hobson forced a decent stop out of Bastock after outpacing the Boston back-line, whilst Tyrone Kirk tested Jan Budtz, who palmed Kirk's effort around the post, for Nathan Stainfield to head well over.
Boston drew first blood when they broke swiftly from a corner, Staifield launching down field, Danny Sleath getting the space to put in a near post cross, and Marc Newsham beating everybody to the near post to nod powerfully home.
Celtic were unfazed, and came back at Boston, Craig Hobson again beating the offside trap, reaching the ball ahead of Bastock, but firing just the wrong side of the post. Just after, Arthur Gnhoua was brought on for Greg Wilkinson, and immediately set about making a nuisance of himself. He won the ball in the middle of the park, releasing Phil Marsh to run at the Marshall Connor. Marsh beat his man and fired across the face to Steve Brogan running at the far post unchallenged and able to smash home the equaliser.
Celtic finished the half stronger, with Arthur Gnahoua's smashed shot was blocked by Gareth Jellyman's stuck out leg as Boston could not clear a corner, Phil Marsh curled a great effort narrowly wide, and Bastock made a good stop from Phil Marsh's effort right before the interval.
Despite an addition of five minutes of stoppage time, presumably for every throw in and goal kick, neither team could break the deadlock.
The same was true after the restart, Marsh again testing Bastock as he raced past the offside trap and Bastock saved well. At the other ended Ian Ross fired a free kick wide, and Sleath missed a glorious opportunity. Substitute Spencer Weir-Daley didn't miss his glorious opportunity. When the Celtic back line seemed intent in playing it out of the six yard box. Weir-Daley still had work to do, but his turn and shot from eight yards beat both Andy McWilliams and Jan Budtz.
It could have been three seconds later, but Jan Budtz made an excellent save from Ben Miles half-volley.
However, when Ben Fairclough's shot hit Rhys Meynell's arm in the box, it was adjudged deliberate and Marc Newsham stepped up to take the penalty. Budtz guessed the right way, but the shot was too powerful to hold.
From somewhere the referee found seven minutes of stoppage time. This was all needed for Celtic to finally break their way through the well marshalled United rear-guard, but they couldn't keep up with Hobson, who latched onto Gnahoua's blocked rocket of a shot, and knocked it past Bastock for a simple finish. There was no more magical time to be added on, so Celtic were unable to fashion an undeserved unlikely equaliser.