East Bengal did the league double over cross-town rivals Mohun Bagan for the first time in 15 years and a first in the I-League era as the Red and Golds ran out 2-0 winners at the Salt Lake Stadium on Sunday.
Jaime Santos (35') and Jobby Justin (75') scored in either half to hand East Bengal the ultimate bragging rights in the Kolkata derby.
Striker Henry Kisseka slotted into a makeshift central midfield role to compensate for Yuta Kinowaki's late retraction from the starting XI as the Japanese pulled up during warm-up. Meanwhile, Pintu Mahata returned to the lineup after being sidelined for almost seven weeks.
Alejandro Menendez had to make an enforced change with Manoj Mohammad suspended. Kamalpreet Singh was ushered in at left-back with Lalramchullova man-marking the returning Sony Norde, in his first derby appearance since December 2017.
The derby was off to an entertaining start with Jobby Justin failing to connect from inside the box as early as in the seventh minute of the game. Bagan had half an answer within the first quarter of an hour as Eze Kingsley failed to tap into space from Norde's cross.
This was followed by a contentious two-footed challenge from Shilton Paul on Justin after the goalkeeper failed to communicate with Abhishek Ambekar while clearing the ball inside the box. Referee CR Srikrishna turned a deaf ear to appeals from the East Bengal players.
Even Sony Norde was on the end of a controversial decision when Kamalpreet's mistimed challenge had the Haitian on all fours in the 24th minute and the referee did not point to the spot.
The Red and Golds took advantage of Bagan's lack of clarity in the final third and with some aplomb. Kingsley failed to steer clear a long punt from Chullova near the touchline. An onrushing Justin snatched the ball away from the Nigerian and ran past Abhishek Ambekar to lay the ball for Santos. The Spaniard then wrong-footed Gurjinder Kumar inside the box and with ease, slammed the ball past Shilton to break the deadlock.
Goalscorer Santos had a lucky escape six minutes after the change of ends as he appeared to have strangled Aser Dipanda inside his own box with the help of Johhny Acosta. However, the referee did not show any cards.
Mohun Bagan then had a goal disallowed in the 53rd minute with linesman Antony Abraham raising the flag for offside.
From the corner, Kingsley's effort ricocheted off the bar and Darren Caldeira had headed it for Dipanda to finish but the ball took a deflection off the former ATK man who stood ahead of the Cameroonian, before it went into the net.
Khalid Jamil had no match for Menendez's tactical superiority as the fluidity in attack continued to flummox the Bagan defenders throughout.
The winner of the night came through a set-piece where Lalrindika Ralte's pinpoint left-footed corner kick was headed in by Justin, bringing up his eighth goal of the season.
Jamil had given up on all hopes of a comeback when he chose to bring in Tirthankar Sarkar for the last ten minutes, a player who had hardly any game time under his belt.
East Bengal kept their hopes in the title race alive as they closed the gap with league leaders Chennai City to five points. They remain fourth on the table with 25 points.
Mohun Bagan, having played a game more are four points behind East Bengal and languish at the sixth spot.