Saturday’s vital equaliser came from the head of a former Tannadice defender who was savagely criticised by Tangerine supporters during two years at the club.
Donaldson considered quitting football in his early 20s after the unsavoury experience, but has rediscovered his love of the game over two seasons under John Robertson in Inverness.
The 24-year-old, who knocked the stuffing out of Ayr United with that first goal of the season, has had his say before about the Tannadice ordeal.
But the Edinburgh-born centre-half admitted: “There will be an added incentive for me.
“I’ve spoken plenty about my time at United and I’ve given as good as I got, but we’re looking forward to Tuesday. Hopefully we can get a positive result for the second leg.
“It’s another hurdle in front of us to where we want to go but we’re looking forward to it.”
The draw with Ayr was Caley Thistle’s 50th competitive game of a gruelling season.
By the time they complete the two-leg play-off semi-final with United, they will have played 14 matches in less than two months.
The SPFL Premiership play-offs seem designed to beat smaller clubs to a pulp in time for the final, but United at least will have had nine days’ rest.
Home manager John Robertson called the latest Tuesday-Friday challenge “ludicrous” scheduling, given the matches could easily have been played on Thursday and Sunday.
Ian McCall, the beaten Ayr manager, has described the play-offs as a pathetic carve-up and “anti-sport”.
But the bad news for United is that Donaldson is convinced Caley Thistle are taking it all in their stride. He stressed: “There are two ways of looking at it. When I played Falkirk in the play-offs with Dundee United our thinking was we’d played two games and were ready to go, while they had just been training all week.
“Sometimes going game to game and knowing exactly what you have got to do works better. But United will be fresher and have had a full week to prepare.
“Anything else is just excuses. We’re fine. This will be two games between two teams who want to be in the Premiership and that’s all that matters.”
An emotional McCall hailed two incredible seasons and spoke of how the experience had re-ignited his own ambitions in management.
The Ayr manager, pictured, said: “I’ve been very proud of the last two years. Ayr United have given me my drive and all my ambition back.
“It wasn’t so long ago that every club in Scotland wanted me when I went to Dundee United, so I don’t want to build a team to be eighth.
“I want to build a team to win the league, and we’ll see if I’m able to do that.”