ATKMB looked the likelier of the two teams to take the lead in the opening exchanges, with the Mariners needing two goals at least to make a comeback.
The two teams will go up against each other again on Wednesday for the second leg
The result means Mumbai sit at the top of the pile with 16 points from eight games but have drawn after their 0-3 loss to Kerala Blasters. NorthEast United remain ninth having eight points from nine games.
Nassiri is son of former East Bengal legend Jamshed Nassiri, who was known for his powerful headers in the '80s.
FC Goa missed the chance to enter the second leg of their Indian Super League (ISL) semi-finals with an advantage as they squandered a lead twice in their 2-2 draw against Mumbai City FC
Spanish midfielder Javi Hernandez scored two stunning goals as Odisha FC made a winning start to their Hero Indian Super League campaign with a 3-1 victory over Bengaluru FC, at Tilak Maidan stadium in Vasco, Goa, on Wednesday.
Bengaluru FC snapped a seven-game winless run to record a 4-2 victory against Chennaiyin FC
It was all Hyderabad after the first goal as they dictated the game and kept pressing the NorthEast United backline.
The Nizams remain unbeaten in the competition while JFC are yet to taste victory.
I-League: Churchill Brothers hand Mohammedan Sporting first defeat of season
All eyes were on the 131-year-old club Mohun Bagan as they were making their ISL debut following their 'marriage' with three-time defending champions ATK.
For Mumbai, they stretched their unbeaten run to 11 matches as they now have 29 points from 12 matches.
ATK Mohun Bagan started off with a more positive intent and dictated the pace of the game
Hyderabad made a disastrous start to the game as Chinglensana Singh was sent off as early as the fifth minute.
A brace from Fran Sandaza (58, 63') and goals from Aridane Santana (86') and Joao Victor (90') helped Hyderabad climb to third on the league table.
I-League set to resume in early March.
Jamshedpur keeper TP Rehenesh was called into action early on, forcing a fine save from Lallianzuala Chhangte.
Goals from Matti Steinmann (6th) and Anthony Pilkington (68th) secured the victory for SCEB
Khalid Jamil also created history by becoming the first Indian to coach three or more league games and guide a side to the playoffs.
ATKMB dominated the early exchanges and constantly raided the opposition box. However, Odisha did well to close down the spaces and keep things tight at the back.
NEUFC eventually grew into the game and fashioned better chances in the second quarter of the opening half. They had a penalty claim denied after the half-hour mark.
Goa were reduced to 10 men in the second half after Ivan Gonzalez received marching orders following two yellow cards within a span of seconds.
It was one-way traffic in the opening half with Hyderabad all over Odisha. Their dominance saw them head into the break with a one-goal advantage after creating numerous chances.
NEUFC could have doubled their tally soon after the half-hour mark had Suhair VP converted his chance. Rochharzela whipped a cross for the unmarked striker in the box, but he cushioned his header over the crossbar.
It was Odisha, which started better, enforcing a corner in the third minute but Kerala scored the opener much against the run of play.
The Mariners looked the better side and had the best chance of the first-half in the 40th minute but Williams' powerful left-footer rattled off the upright.
The result meant ninth-placed Kerala are now level on points with SC East Bengal, who have a game in hand.
Chennaiyin's defense was a tough nut to crack as Eli Sabia and Vishal Kaith came with crucial interceptions and blocks to deny Sunil Chhetri and Paartalu.
The Sergio Lobera side now have six points from three matches, while SC East Bengal remained at the bottom of the table, yet to open their account in their debut ISL season.
India international Anirudh Thapa scored in the first minute to set up Chennaiyin FC's 2-1 win over Jamshedpur FC in an Indian Super League match, in Vasco, on Tuesday.
The committee found Mukhi guilty on the basis of the evidence presented by him, his admissions and the statements of the manager of Under-16 AIFF academy in 2015.
Here is a round-up of results from the ISL and I-League matches played on Monday
Chhetri was shown the first yellow in the 22nd minute after bringing down Anirudh Thapa, something he repeated on the same player after nine minutes to be sent off.
Coach Manuel Marquez seemed to have prepared well for the Mumbai test. The Nizams pinned their opponents with their high pressing approach, thus nullifying Mumbai's danger.
Portuguese forward Goncalves opened the scoring in the 15th minute, before putting Chennaiyin two-up by converting a penalty in the 21st minute.
This result meant a win for ATK Mohun Bagan against Hyderabad FC on Monday would ensure them of the League Winners Shield and a maiden AFC Champions League spot.
Bengaluru took just three minutes to register their first shot on target. Kristian Opseth's free-kick nearly curled into the bottom corner, only to be kept out by a diving TP Rehenesh.
NEUFC started the game at a furious pace and only needed nine minutes to come up with the first goal. Ashutosh Mehta found Machado with an accurate cross and the latter hit it first time past a diving Arshdeep Singh.
The victory helped Mumbai rise to fourth in the league standings with 23 points from 15 games and stay in reckoning for a play-offs berth with three more games left.
Goa were keen to impose themselves on the Highlanders and came close in the fifth minute. Fernandes played a long diagonal pass from inside his own half to find Mendoza on the flank, but the latter shot straight at keeper Subhasish Chowdhury.