The 33 year old, who is searching for a first win on American soil for five years and who will go third in the Official World Golf Ranking with a win in the competition, beat Moore 5 and 4 to send out an ominous warning to the remaining members of the field.
The win was his second-largest at the competition, not quite matching his 6 and 5 success over Robert Allenby a year ago, but that will have mattered little to the Ryder Cup star as he rarely gave Moore a chance.
He was four shots up on his opponent at the turn after five front-nine birdies, and carried on in a similar vein on the back nine, wrapping things up with a 15 footer with four holes to spare.
The one hole Moore did manage to win after the turn could also have gone Donald's way, with him chipping in from off the green on the par five 11th, having driven into the sand.
"I`ve been working hard and it`s nice to see the work paying off. I made a bunch of birdies and made it hard for Ryan," Donald said.
"You do the same things, try and hit it close, give yourself opportunities and put pressure on your opponent."
Donald will face another American in Matt Kuchar in the semi-finals later.
Kuchar overcame Y E Yang 2 and 1 to build on his victory over Rickie Fowler, knocking out Graeme McDowell`s conqueror in the process.
He had led by four at the turn, but after Yang dug in to win on the tenth and 13th holes, Kuchar held his nerve to chip onto the 17th green and then putt from three feet to win the match.
Martin Kaymer, knowing he will replace Lee Westwood as the world`s best player if he makes it through to the final, had to cling on to get the better of Ryder Cup teammate Miguel Angel Jiménez.
The German did not drop a shot on the front nine and was four up with four to play before Jiménez mounted a rousing fightback.
Kaymer had chances to halve the hole and win the match on the 15th, 16th and 17th holes but failed, leaving the Spaniard to birdie two of them and win all three to take the match down to the final hole.
Kaymer looked to have driven himself into a dangerous position, but a fine recovery with his third shot forced Jiménez to concede, giving Kaymer the win 1 up.
Kaymer will face Bubba Watson after a dramatic clash with JB Holmes.
Holmes led by five after ten holes, but Watson mounted a stunning fightback to level the tie and send it to a one-hole play-off.
He actually had chances on the 16th and 17th holes as well, before taking the match to an additional hole on the 18th.
With both men taking their time the last two holes lasted for well over an hour, before Watson landed a four footer to take the game on the play-off.
"You have to play all 18 holes and I didn`t finish off as I needed to. It's golf, it happens to somebody every year," Holmes said.