McIlroy missed the cut, his second straight, after his game disintegrated again. The U.S. Open champion made seven bogeys and two double bogeys in a 7-over 79 to finish 9 over -- a massive 21 strokes behind Morrison.
Only 13 players in the 150-man field have returned scores higher than McIlroy in this tournament, with a quarter of the field yet to finish. The cut is projected at 1 over.
Morrison, who played cricket for England at the youth-team level, had four birdies in the five holes around the turn to put him in the lead. Morrison holed an eagle putt at the par-5 last hole for the second day running, putting even more distance between himself and his rivals.
"Definitely one of the best rounds I've ever had and probably one of the easiest, funnily enough," said Morrison, who lives a few miles away from Wentworth. "It felt easy. I wish golf was like that every day."
Peter Lawrie of Ireland (71), who shared the overnight lead with Drysdale at 6 under, and Alvaro Quiros of Spain (70) were five shots back. Justin Rose shot a 71 and is tied with seven others at 6 under.
Donald, the reigning champion, must finish eighth on his own or higher to leapfrog McIlroy and take the No. 1 world ranking.
"I'm feeling strong on the greens," Donald said. "Every time I've had opportunities, I'm seeing the line and got the speed down and making some good putts."
Morrison's only tournament win came at the Madeira Islands Open in 2010. A second victory would be a great way to sign off for a break ahead of the birth of his first child next month.
Information from The Associated Press was used in this report.