The Pilgrims trailed to Harry Chapman's 21st minute opener - but responded in first half stoppage time through Maguire, who had stepped off the bench to make his first appearance since August 9.
Donnelly and Hiwula added further goals in the 54th and 74th minutes respectively - although United's afternoon was tarnished by a late knee injury sustained by Jordan Cropper, after Jordan Richards had limped off with a hamstring issue at the end of the first half.
The lunchtime kick-off saw United quickly pressed back into action following their 0-0 draw against Forest Green Rovers on Wednesday night.
They almost took a 10th minute lead when United countered quickly for ex-Pilgrim Tiernan Brooks to make a smart save to deny Cropper.
Gateshead took the lead despite Rhys Lovett's low save to deny Kyle Hurst, with CHAPMAN slamming home the rebound from close-range.
United thought they had levelled on 36 minutes when Lenell John-Lewis finished off a smart United move, only for Steve Wade's offside flag to intervene.
Richards limped off with a tight hamstring in first half stoppage time - and his replacement MAGUIRE made the dream impact after touching home Matty Carson's low cross from the left.
Brooks made a brilliant save to deny John-Lewis two minutes after the break but United's move into the lead did not take too much longer, with Connor Teale's raking througball finding DONNELLY who nutmegged ex-Pilgrim David Ferguson and beat Brooks at his near post with a smart, rising finish.
Lovett stretched high to deny Hurst and it proved crucial for the Pilgrims, with Donnelly and Maguire combing well to tee the ball up for Carson to deliver a brilliant cross for HIWULA to slam home at the back post.
Lovett made a further save to deny Lucas Lowery late on, but United's main concern in the closing stages was the injury sustained by Cropper, who will be assessed further over the weekend.
Gateshead (3-4-3): Tiernan Brooks; Fenton John, Will Flint, Connor Pani (Lucas Lowery 41); Josh Home, Curtis Edwards (Callum Bone 58), Jacob Butterfield, David Ferguson; Kyle Hurst, Frank Nouble (Callum Johnson 83), Harry Chapman. Subs (not used): James Blakey, Jake Lish, Preston Leech (gk).
Boston (4-3-2-1): Rhys Lovett; Jordan Cropper (Ben Grist 90), Connor Teale, Zak Mills, Alex Lankshear; Greg Sloggett, Jordan Richards (Frankie Maguire 45), Matty Carson; Dylan Hill, Owen Hampson (Kieren Donnelly 46); Lenell John-Lewis (Jordy Hiwula 68). Subs (not used): Michael Kelly, Rocco Coyle, Bobby Jones (gk).
Referee: Garreth Rhodes.
Attendance: 773 (162 visitors).
PIC: Chris Bray.