The sought after striker pickpocketed a defender on the right touchline to release Shaun Beeley down the right and his pull back was fired home by McDonald on the hour mark.
He then brilliantly pulled down a long ball over the top under pressure by Elliott Percival and smashed a shot past Liam Castle in the Barwell goal to make the points safe.
What would be an open first half started with two decent openings for Jamie McDonald, who twice got goal side of his man in the box before some scrambling defence got the ball away.
Barwell too were enjoying some success, largely on the counter attack, without troubling Luke Pilling in the Warrington goal, though a defensive header by Liam Goulding had some hearts in mouths as it dropped on the roof of the goal.
Matthew Stenson, who would be forced off injured in the first half, won the ball in midfield and took the ball forward to create a half opening for Barwell, but Goulding was there to intercept.
The clearest opening for the hosts came on 21 minutes when Devarn Green got down the left hand side and his initial cross was punched away by Castle under pressure from Joe Piggott, before the ball made its way back to Green and his shot was deflected over the bar.
Pilling was called in to action eight minutes before the break, getting down sharply to save a good effort by the eye-catching Brady Hickey from a Barwell corner.
But generally the Yellows were having the better of the play and they could have taken the lead five minutes before they did when they had three opportunities off the same corner.
A half clearance was driven goalwards by Steve Jennings to force a smart stop by Castle and from the rebound McDonald hit the bar from point blank range, before Castle held on to Jack Higgins’ follow up.
That would prove to be the last of Barwell’s resistance and once McDonald broke the deadlock, the hosts didn’t look like dropping any points on the afternoon and he added his second on 69 minutes to provide an extra cushion.
With games off elsewhere, the win consolidates Warrington’s second place position in the league table.