Diane struck in the 19th minute of the Group A clash at Al Gharafa Stadium and the hosts could even afford to see Juninho miss a penalty in the second-half as they collected their first win of the campaign and inflicted Sepahan’s first defeat in the process.
Sepahan striker Ibrahima Toure had a shot from inside the Al Gharafa box in the second minute as the visitors began strongly but goalkeeper Qasem Burhan was alert enough to push the ball away for a corner.
Four minutes later, Sepahan had the ball in the net through Reza Enayati’s spectacular scissor-kick but the effort was ruled out as the Iranian striker fouled Al Gharafa's Otman El Assas in the build-up.
Bilal Mohammed then delivered a curling cross into the box but Hamed Shami's header from close range kissed the crossbar and flew to safety.
The hosts then took the lead in the 19th minute when Juninho found Diane unmarked close to the Sepahan box and the forward went past two defenders before firing past goalkeeper Mahdi Rahmati, who had come out to narrow the angle.
In the 32nd minute, Sepahan captain Moharram Navidkia almost scored direct from a corner but the ball was helped over the crossbar to safety by Burhan.
El Assas was then forced off for more than five minutes after he exited the pitch to seek treatment for a blow to the back of his head. The midfielder returned with a heavy bandage across his head as Al Gharafa battled to keep the lead in the first-half.
The second period began at ferocious pace as the visiting side mounted a series of attacks to try and find an equaliser but it was Al Gharafa who nearly scored a second time as Ahmed Fares' fierce shot from close range was blocked by keeper Rahmati.
Juninho then exhibited great calm under pressure when he stole the ball from the feet of Toure with the striker set to pull the trigger from six yards out.
The Brazilian was not so cool in the 64th minute, however.
Abdulaziz Al Shammari was recklessly brought down by Ehsan Haji inside the Sepahan box. Juninho went to Rahmati’s right with the penalty but the keeper was equal to the effort.
In the 73rd minute, Sepahan's Mohsen Bengar curled in a swinging free-kick from distance that team-mate Enyati diverted just too high.
Sepahan pressed for an equaliser but the home team - after a few tense moments - managed to hold on to their lead.