The all-important goal came in the 33rd minute when Ambekar's clearance off a Phool Chand Hembram cross turned suicidal.
Maharashtra put up better performance in the second half but didn't make any gains from the numerical advantage after referee Ramaswamy Srikrishna gave marching order to Railway's Shabaz Pathan at the stroke of an hour.
Maharashtra failed to cash on the advantage as they went all out in search of the equaliser but failed to beat as rival goalkeeper Owais Khan brought off some impressive saves to deny former I-League player Vijith Shetty.
Railway now have three points from three matches after their first victory. Maharashtra are yet to open their account after two matches.
In another match at Bambolim, Kerala snatched a point from the jaws of defeat as substitute Muhammed Parakkottil banged in two goals in the last 10 minutes to earn a thrilling 2-2 draw against Punjab.
In a match that came alive in the second half, Punjab were 2-0 up with just 10 minutes of play left. However, Kerala came from the death to score two late goals and gain a valuable point that kept them firmly in contention for a semifinal berth.
Punjab produced some fine counter attacking play to go 2-0 up within first 20 minutes of second half. First, a strong cross from the left by Amandeep Singh went dangerously close to the goal and Kerala defender Sherin Sam knocked it into his own net while trying to clear it.
In the 57th minute, a lovely diagonal ball across the Punjab midfield found Manvir Singh a lot of space on the left. He kept his composure, feigned two defenders and neatly placed the ball past an onrushing goalkeeper into the open net.
With nothing to lose, Kerala coach V P Shaji brought in Muhammed Parakkottil. And the Under-21 youngster did not disappoint his coach.
Two minutes before the end of regulation time, a brilliant cross by Jobby Justin found Parakkottil who sent a powerful header that gave Punjab keeper Paramjit Singh absolutely no chance of saving it.
With seconds to go before the final whistle, Jobby Justin turned provider again when flicked header found Parakkottil who was at the right place at the right time to deflect the ball into the Punjab goal.
With this draw, Kerala have four points from two matches while Punjab, with five points from three games, need a win in their final match against Maharashtra to have any hopes of reaching the semi-finals.