The forward’s header put his time back into the lead after Chris Maguire’s opener was cancelled out by Jordan Preston.
Josh Scowen added a third soon after Parkinson’s change XI overran a tiring home side.
A comfortable start to the pre-season campaign was marred only by a first-half injury to talented attacking midfield Elliot Embleton.
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Parkinson revealed before the game that he would not be naming what he imagined to be his strongest side, opting instead for a blend of youth and experience.
With Sunderland set to play another friendly in the near future, the aim was to play one side for 60 minutes and another for 30, before flipping it next time they’re in action.
Sunderland also named a trialist, understood to be Kosovan defender Arbenit Xhemajli, in their squad for the afternoon.
The pace to the game was understandably sedate to begin with, the Black Cats playing their first game against external opposition in almost six months.
It took a while for Sunderland to take control but gradually they began to dominate possession, and went close to an opener when Tom Flanagan released Denver Hume with a superb through ball.
Hume flashed a low cross to Chris Maguire, who took one touch before firing just wide on this left foot.
Gateshead were content to counter, and should have gone ahead when indecision in the box allowed Greg Olley to create room for a shot.
His effort looked destined to hit the top corner but Lee Burgemade a superb save, flying to his left and pushing the ball past the far post.
The home side saw their rhythm disrupted when star striker JJ O’Donnell suffered an injury, the Black Cats taking the lead minutes later when Hume again surged towards the box.
He was brought down on the edge of the box; Maguire stepping up to curl the free-kick into the corner.
Though the pace of play reflected a pre-season opener, Sunderland looked comfortable on the ball and Charlie Wyke, usually so often the focus of early balls forward, had little influence.
Gateshead’s equaliser came from nowhere, a moment of indecision from George Dobson and Flanagan turning over possession and leaving their team caught of shape.
Mike Williamson’s side took the chance superbly, Jordan Preston making a good run and pushing a composed finish past Burge.
Sunderland continued to dictate play but produced little, though Bailey Wright had a firm header from a corner pushed away from goal.
Parkinson’s side ended the half with an injury concern, Elliot Embleton heading straight down the tunnel after picking up a knock just as he was beginning to show his composure in possession.
That gave an unexpected chance to young midfielder Dan Neil, who showed some clever touches.
Parkinson also used the half-time interval to introduce Xhemajli, who cut an imposing figure as he slotted into the left centre-back position.
The 22-year-old was almost on the scoresheet with the first meaningful effort of the half, making a good run to escape his marker at a corner, before finding the far post with a thumping header.
Parkinson’s wholesale changes brought an immediate lift in tempo, substitute Grigg twice making good runs in behind that didn’t quite create an opening.
The gaps in the Sunderland squad were also clear, with Neil dropping back to left wing-back after Hume’s departure.
The home side were starting to look leggy and Parkinson’s new-look XI were ready to pounce.
Jack Diamond, slotting in at right wing-back, produced a superb cross with twenty minutes to play, the lively Grigg rising highest to head back across goal and into the far corner.
Within minutes, Grigg was using his chest well to lay a powerful diagonal into the path of Josh Scowen. Scowen rifled in a low and firm half-volley that left the goalkeeper with no chance.
By now Sunderland were dominant and should have had a fourth, Jordan Willis heading wide at the front post from a Lynden Gooch corner.
Gateshead rallied to forge another strong save from Burge in the closing stages, but Sunderland ended the contest deserved and comfortable winners.
Starting XI: Burge; O’Nien, McLaughlin, Wright, Flanagan (Xhemajli, 45), Hume; Dobson, Leadbitter, Maguire, Embleton (Neil, 39); Wyke
Change XI: Burge; Diamond, Willis, Feeney, Xhemajli, Neil (Hackett, 83); Power, Scowen; O’Brien, Gooch, Grigg