Mosta obtained three precious points in their quest to move away from the red zone, by beating direct opponents and bottom placed San Gwann with the odd goal in three.
This third consecutive defeat for Doncic's side leaves San Gwann firmly anchored at the bottom of the table, with their aspirations fading away.
The first half was well played by both sides with Mosta showing the better ideas and missing the best chances. Mosta were without Philip Camilleri and Steve Borg, with Anthony Ewurun and Carlos Camenzuli as their strikers.
However the best ideas came from Brian Agius whose non stop running down the left flank was a constant menace to the San Gwann defence well marshalled by Arnold Galea.
On their part San Gwann had Stajic and Decesare in attack, but the two strikers found little space in the Mosta defence, with Daniel Theuma and Brian Galea forming a solid pair at the back.
Mosta went close on seven minutes when San Gwann goalkeeper Justin Spiteri had to dive to save a Melvin Farrugia scorcher from the edge of the area. Mosta's best chance came on the half hour with Anthony Ewurun face to face with Spiteri, but the ex-St George's and Marsa player shot weakly in Spiteri's waiting hands.
Minutes later San Gwann had two dangerous breaks with Decesare blocked by goalkeeper Galea in the first chance, and with the same Decesare shooting slightly wide in the second.
Near the end of the first half Mosta missed two easy scoring chances with Ewurun lobbing slightly over the bar and Brian Agius going very close through a close range header that went inches wide.
At the start of the second half Mosta forged ahead with a Melvin Farrugia shot from the edge of the area that beat Spiteri. San Gwann scored immediately but their goal was disallowed for a very dubious offside infringement.
On 53 minutes Ewurun was put through by Charles Sciberras, but the Mosta striker was brought down inside the area by the San Gwann goalkeeper. However from the resultant penalty taken by Daniel Theuma the ball was deflected by Spiteri against the base of the upright. Mosta paid dearly for this miss as San Gwann obtained the equaliser seconds later when Nebiosa Stajic scored with a grounder following a Decesare through pass.
San Gwann were playing better now and had some favourable situations in front of the Mosta goal, but failed to capitalise. Fifteen minutes from time, Mosta were back in the lead when substitute Lydon Cilia crossed to Ewurun who scored from close range.
San Gwann pressed forward in the dying minutes with Mosta goalkeeper saving a dangerous Mauro Brincat freekick. Six minutes from time a Decesare header went slightly over the bar.