This week Nole has reached a total of 171 weeks at #1 that puts him ahead of McEnroe for 5th place.
Most Weeks at #1
1. Roger Federer 302
2. Pete Sampras 286
3. Ivan Lendl 270
4. Jimmy Connors 268
5. Novak Djokovic 171*
6. John McEnroe 170
7. Rafael Nadal 141
8. Björn Borg 109
9. Andre Agassi 101
10. Lleyton Hewitt 80
http://www.atpworldtour.com/en/news/djokovic-171-weeks-no-1-emirates-atp-rankings
Most Weeks at #1
1. Roger Federer 302
2. Pete Sampras 286
3. Ivan Lendl 270
4. Jimmy Connors 268
5. Novak Djokovic 171*
6. John McEnroe 170
7. Rafael Nadal 141
8. Björn Borg 109
9. Andre Agassi 101
10. Lleyton Hewitt 80
http://www.atpworldtour.com/en/news/djokovic-171-weeks-no-1-emirates-atp-rankings