The win at the Jawaharlal Nehru Stadium ensured that the Mariners extended their undefeated streak against the Blasters to five games in the ISL.
The noise inside the Blasters' fortress reached a crescendo when Ivan Kaliuzhnyi put the hosts in front just six minutes into the game.
Early pressure paid off as the Ukrainian combined well with Sahal Samad on the right before beating Vishal Kaith at the near post.
The stands were silenced in the 26th minute after Boumous sprinted down the left flank and skipped past Ruivah Hormipam before unselfishly putting it on a plate for Petratos to tap the equaliser in.
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