Javad Maheri sealed Sepahan's 1-0 away win against Rah Ahan in the 12th minute, to send the Isfahan side to the IPL top spot with 25 points out of 14 matches.
Esteqlal, which is in second place with 24 points from 13 matches, will face fifth-placed Zob Ahan on Tuesday.
Later on Monday, Persepolis beat Teraktor Sazi 2-1 thanks to strikes by Mojtaba Zarei (67') and Hawar Mulla Mohammed (86').
Farhad Kheirkhah's injury-time goal, little consoled thousands of Teraktor Sazi fans, who had come all the way form the northwestern city of Tabriz to Tehran's Azadi Stadium.
A recent online poll by the website of the popular Iranian sports show 90 showed that the Tabriz club's fans were considered the staunchest among IPL clubs.
Persepolis moved to the fourth place with 23 points, behind Paykan, who enjoy better goal difference.
In other matches, Steel Azin was held to a 1-1 against bottom-placed Abumoslem to stand in fifth place with 21 points. Mes defeated Saipa 3-2 in Sunday's goals galore game.