Skipper Jaydev Shah won the toss and decided to bat, but the hosts had a poor start as the visitors' seam bowlers Krishnakant Upadhyay and Sanjay Bangar took two wickets each, reducing Saurashtra to 90 for four at one stage.
However, Jadeja and Kotak came to team's rescue by adding 137 runs for the fifth wicket.
Jadeja, who took 142 balls to complete his century, was batting on 111 (224b, 10X4, 2X6) and Kotak was batting on 53 (133b, 9X4) when stumps were drawn on day one.
For Railways, Upadhyay and Bangar took two wickets each, giving away 53 runs and 46 runs respectively.
Brief Scores 1st innings: Saurashtra 227 for 4 in 90 overs (Ravindra Jadeja batting 111, Sitanshu Kotak batting 53, Krishnakant Upadhyay 2 for 53, Sanjay Bangar 2 for 46).