Donaldson's stunning approach to the 15th green and Keegan Bradley's subsequent concession ensured the Welshman a 4 and 3 win on his Ryder Cup debut - enough to put the title out of USA's reach.
Having won three of his four matches at Gleneagles - losing the other - Donaldson enjoyed a strong tournament bow as Europe won the competition for a third consecutive time.
The 38-year-old struggled to sum up his emotions, after wins from Rory McIlroy, Graeme McDowell and Martin Kaymer put Europe on the verge of success, but expressed pleasure at his winning contribution.
"I knew obviously I'm 4up with four to play there and hit a really good tee shot down 15 there," the Welshman said.
"[It was] just a perfect yardage and [it was the] wedge shot of my life to close the game out.
"I can't really put words to it. It's unbelievable. Obviously I knew it was all getting tight there at the end, but it's all getting tight at the end, and everybody was obviously building at my group.
"I was just trying to not spend too much time looking at the scoreboard and just concentrate on my match and that's what I did, and was able to do it well enough to close it out."
Donaldson paid tribute to the team atmosphere fostered by captain Paul McGinley - the Irishman adding to the three Ryder Cups he won as a player with this triumph.
"The lads have got on so well all week. It's been great craic in there," Donaldson continued.
"It's just an incredible week. It's hard to describe how good it is. There's nothing else like it in golf.
"It's just a total one-off. It's just a huge, huge thing, and it's just been amazing to be a part of it."