Electing to bat, Hyderabad posted a challenging 191 for 4 courtesy Williamson's 89 off just 51 balls and his 136-run stand for the second wicket with opener Shikhar Dhawan (70), and then restricted Delhi to 176 for 5 to maintain their unbeaten run at home.
With their fourth successive win at home, Hyderabad jumped to second spot with eight points from six matches, from four wins and two losses.
But once Samson and Nair were out, Delhi innings lost way and the asking rate piled up. They needed 65 from the final five overs but could only score 49 with the Hyderabad side bowlers coming up with a fine bowling show at the death overs.
Needing 24 runs from the final over, Delhi made a valiant attempt but ended up 15 runs short in the end.