Extra-time was looming in Wednesday night's Scottish League Cup tie at Cappielow Park when McKendrick ordered a Stevie May free-kick to be retaken in the third minute of injury time, due to encroachment by Morton forward Nacho Novo.
May's second effort was spilled by Greenock goalkeeper Nicolas Caraux and McDonald pounced to bundle the ball over the line and book a Scottish Communities League Cup semi-final spot.
Morton boss Allan Moore was so angry he refused to speak to the media afterwards but Wright said: "He was too close to the ball, that's what the players were saying I haven't seen it.
"Nigel Hasselbaink was booked for leading with his arm and another player wasn't so there are things given and not given.
"Allan will have a different perspective but if he is too close to the ball he is too close to the ball and the referee has to give it.
"If a referee somewhere else tonight doesn't give it, is irrelevant. They have a difficult job to do. I think they handled the game well.
"May made it really difficult for the keeper but we had Gary McDonald and another player showing a bit of desire to get on the follow up so I was really pleased."
Morton players surrounded the referee after the game but skipper Mark McLaughlin tried to take the sting out of it all afterwards.
He said: "I didn't think there was much in the free-kick and obviously after that it was disappointing.
"I thought it was harsh but the referee has got to make the decision, there and then he felt he made the right decision.
"There were many people having a go at him, not in a disrespectful way, they were expressing our disappointment.
"We didn't think it was a free-kick to begin with and we didn't think Nacho had encroached that much, he was only a yard away from me.
"I thought it was a bit harsh but we move on to the next game. It probably sums up our season in terms of luck.
"We thought we battled well and held our own against a good Scottish Premiership side."