In reply to Saurashtra's first innings total of 207, Gujarat managed to take a slight edge.
Resuming on three for no loss, Gujarat were struggling at 136 for seven at one stage, despite a 46-run partnership for the second wicket by opener Priyank Kirit Panchal (38) and one-down batsman Bhargav Merai (22).
From 72 for one, Gujarat lost six wickets for an addition of just 64 runs and were at the risk of conceding the first innings lead.
Smit then put on another 41 runs with Pranjal Sutaria (12 not out) for the ninth wicket to give his team an important first innings lead.
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Batting patiently, Smit spent 233 minutes on the crease, even as wickets kept tumbling at the other end.
For Saurashtra, Dharmendrasinh Jadeja was the pick of the bowlers with figures of five for 74.
Saurashtra 1st innings: 207 all out
Gujarat 1st innings: 248 all out in 90 overs (Smit Patel 105, Priyank Kirit Panchal 38, Rush Kalaria 31; Dharmendrasinh Jadeja 5/74).