A goal either side of half time condemned the Bees to defeat against the early National League leaders Torquay United.
After an even start at a rainy Hive London, it was the visitors who took the lead, as Ben Whitfield finished an incisive Gulls breakaway.
The Bees reacted well to falling behind and nearly levelled through new man Courtney Baker-Richardson, but the ball was nipped off his toes at the crucial moment, after a good ball from Mason-Clark.
Liam Daly was next to have a chance for the Bees as his towering header forced MacDonald to punch clear.
Torquay were a threat themselves and almost doubled their lead through Whitfield but his effort was wide of the near post.
The last chance of the half fell to the Bees, but JJ Hooper couldn't get Myles Judd's delicious cross on target.
The second half saw a continued response from Tim Flowers' side, the introduction of Michael Petrasso saw the Bees try to get at the league leaders.
Scott Loach made a big stop with 23 minutes left on the watch, as Whitfield broke clear but Loach stood strong to deny him one-on-one.
Moments later Rob Street founds a gap in the Bees backline, but he couldn't convert his effort on target.
In what was his first appearance in over 10 months, it was an impressive debut from Courtney Baker-Richardson, he will gain more fitness but had to withdraw just before the hour mark.
The Gulls had an extended spell of possession and found a second goal with seven minutes left on the watch, as Jake Andrews fired in from 20 yards.
The league leaders saw the game out and whilst there was an improvement from the Bees, they couldn't find an all-important result.
There is yet another swift turnaround for the Bees, as they have another game on Tuesday night where they'll make the short trip to Aldershot Town.
Barnet: Loach, Judd, Daly, Richards-Everton, Binnom-Williams; Taylor, Dunne (C), Wordsworth (McBurnie); Mason-Clark (Petrasso), Hooper, Baker-Richardson (Pavey).
Unused subs: Azaze, Kefalas.