Having seen off the challenge of Ryan Moore with four holes to spare in their last-eight tie earlier in the day, the 33 year old, who will go to number three in the Official Golf World Ranking with a tournament win, was up six with nine to play at the turn.
The Ryder Cup star produced a perfect display of putting, birdieing seven holes, including a 25 footer that came in from right to left on the ninth, with Kuchar's birdie on the par five second stopping him being seven up.
Donald birdied the sixth, seventh, eighth and ninth holes, having previously landed three five footers in a row as Kuchar was left with no answer.
In the other semi-final between Bubba Watson and Martin Kaymer, the pair were all-square after three holes.
Their match started behind schedule after Watson's marathon quarter-final with JB Holmes.
Having trailed Holmes by five shots, Watson roared back to take the match in a play-off.