At stumps, Railways were 86 for two in reply.
Nayar, who came in to bat following Sachin Tendulkar's dismissal scored 107 off 164 deliveries. He struck 10 boundaries and 2 sixes in his knock and survived a chance at 86, when wicketkeeper Mahesh Rawat dropped a sharp chance of India discard Murali Kartik's bowling.
The 29-year old hit a straight six off the same bowler later to reach his 8th first-class hundred. Ajinkya Rahane who was unbeaten on 105 yesterday added 24 more before seamer Krishna Kant Upadhyay trapped him leg before.
Railway lost both their openers Shivakant Shukla and Amit aunikar who couldn't cash in on the dropped catches by Kaustubh Pawar at first slip.
Pawar then made amends and latched onto the catches directed at him off the bowling of skipper Ajit Agarkar.
Mumbai captain Agarkar made a smart move to replace Dhawal Kulkarni at the press box end and found success in his first over by dismissing Paunikar for 9 with the third ball of the over.
Two overs later, he got left-hander Shukla out for 18 in the same manner.
Railways captain Sanjay Bangar added a 55-run partnership with the No 3 Nitin Bhille. Bangar was unbeaten on 36 from 47 balls while Bhille ended the day on 21.
Brief Scores: Mumbai 1st Innings 570 (S Tendulkar 137, A Rahane 129, A Nayar 107, Anureet Singh 3/81, SS Shukla 3/53).
