Sheikh Hamdan's son of Street Cry ran well on debut at Salisbury last autumn and stepped up on that to win nicely under Jack Mitchell.
Jack settled Istinfaar into a good rhythm on the heels of the leaders. He travelled smoothly before making his challenge up the straight.
It was tight between the odds on favourite Alkwan and Sir Michael Stoute's Hakka but Istinfaar proved too strong and went on to win by half a length.
Roger said: "That was pleasing - he is a good looking colt who should improve again when we go up in trip with him."
Istinfaar comes from a Shadwell family which we know well at Kremlin House. His dam Yaqeen was a Stakes winner for the yard and she was a half-sister to the fragile but very talented Alainmaar. Yaqeen's previous foal Tafawuk was also a winner for the stable.