McIlroy rebounded from a 75 in the second round and was a combined 11-under in Saturday's and Sunday's rounds in winning by eight strokes over David Lynn. The margin of victory was the largest in the 94 times the tournament has been contested.
The PGA Championship was the second major tournament title for McIlroy, 23. He won the U.S. Open in 2011, also by a record-setting eight strokes.
Sunday's win moved McIlroy past Luke Donald and Tiger Woods from third to first in the rankings. It is his fourth time to reach No. 1; all have been since March 12. Two of his previous stints on top of the rankings lasted two weeks and the other was a three-week stay.
McIlroy has a rankings points average of 10.354 while Donald slips to second after the last 10 weeks at No. 1, with an average of 9.590. Woods, down one spot to third this week, has an average of 8.709. Donald finished tied for 32nd at the PGA Championship and Woods tied for 11th.
Adam Scott goes from seventh to sixth with an average of 6.134 and Justin Rose, who tied for third at the PGA Championship, jumps from 10th to seventh at 6.124. Bubba Watson (6.112) falls two places to eighth while Jason Dufner (5.929) is down one to No. 9. Steve Stricker (5.782) moves from 11th to No. 10. Matt Kuchar (5.676) falls from ninth to No. 11.