With this defeat Ahli lost whatever slim hopes they might have had of fighting for the Saudi Professional League title this year.
Nasr drew first blood in the 12th minute when Rasyyan Belal's header found the back of the net.
Defender Ovidiu doubled the score ten minutes before time.
Ahli reduced the margin a couple of minutes before time through Hasan Al-Raheb.
Their comeback was short-lived as Raheem Al-Jizawi was shown the red card just before full time.
With this win Nasr move to the second place earning 16 points while Ahli dropped to the 12 position with only seven points.
In the other matches, Ittifaq defeated Al-Raid 3-0 in Buraidah. Ittifaq is third in the standing with 16 points while Al-Raid is in the fifth position with 12 points.
Al-Faysaly defeated Al-Fateh 1-0 in Al-Ahsa. Al-Faysaly jumped to the sixth position with 12 points while Al-Fateh is 13th in the standing with five points only.
Al-Taawon defeated Al-Hazerm 3-0. Al-Taawon is seventh with 11 points and Al-Hazem is at the bottom with only three points.