Naismith and Walker had been absent from the Jambos starting line-up since August due to injury issues, while Mulraney missed around two weeks with an ankle knock.
Yet they showed no ill-effects as Hearts claimed a thrilling triumph over the Buddies at Tynecastle – their maiden league win at home this term and the first time they have hit five goals in a top-flight fixture since battering Inverness 5-1 in August 2016.
Jon Obika and Danny Mullen struck for the Buddies in their most potent attacking showing on their league travels this term but their defensive deficiencies were glaring as they slipped two points adrift at the foot of the table.
It took just five minutes for Hearts to notch the first goal of MacPhee's tenure as temporary boss, with Naismith darting to the near post and instinctively prodding home a fine Andy Irving corner.
The Buddies, who had only found the net twice on on the road in the Ladbrokes Premiership this term prior to arriving in Gorgie, levelled when Obika slammed beyond Joel Pereira following a knock-down by Tony Andreu.
The Jambos restored their lead in fortuitous fashion on the half-hour mark. Uche Ikpeazu latched onto a Naismith flick and prodded the ball beyond the on-rushing Vaclav Hladky, however the effort was not goal-bound until the ball struck McLoughlin and found the net.
A breathless battle took another twist when St Mirren restored parity three minutes later. Christophe Berra inexplicably ducked under a long punt by Hladky, allowing Mullen to scamper clean through and calmly beat Pereira.
However, it was third time lucky as Hearts sought to hold onto a lead. A superb Michael Smith delivery found Bozanic in the box and the Australian playmaker nodded home his first goal of the season.
The capital club extended that advantage just 40 seconds after the break. Again, Smith was the architect as another magnificent delivery found Walker, whose clinical glancing header beat Hladky.
Gloss was applied to the scoreline in sensational style when Mulraney, back in action a month ahead of schedule, climbed off the bench to curl a sumptuous effort into the top corner from 25 yards out.