It was a hard-earned victory on a very bumpy pitch which sealed the top five finish, and United can now concentrate on both consolidating second place behind champions Bonnyrigg Rose and progressing in the two remaining cup competitions.
The first chance of this match fell to Bo’ness after only three minutes when Marty Wright flicked on a near post corner from Brian Morgan. The ball was destined for the top corner but fortunately for Lothian Thistle, Reece Smith was well positioned on the line to head clear.
18-year-old Nail Doherty was the home side’s spark and he should have opened the scoring when he sped clear but with only Andy Murphy to beat he blazed well over from 18 yards.
The second half was three minutes old when United made the breakthrough they craved through Donnelly, after the United skipper seized upon a woefully short Smith back-pass, dummied the helpless Swain and rolled the ball into the empty net.
Donnelly almost doubled his tally when his header from a Morgan corner cannoned against the crossbar and away and shortly afterwards Swain was again called into action as he managed to claw away a mis-hit Morgan cross which was heading in.
Midway through the second period it appeared the Bo’ness advantage would be doubled when referee Calder awarded a penalty after substitute Fraser Keast was brought down by a combination of two defenders.
Up stepped the normally reliable Morgan but Swain was to deny the midfielder with a superb stop low to his right.
The result was finally made safe with three minutes remaining after Fraser Keast grabbed his third goal in four games from a Brian Morgan corner.