Overnight batsman Jackson blasted 11 fours and seven sixes in his 142-ball innings, while No. 9 batsman Jaydev Unadkat scored 91 not out with the help of nine boundaries and four sixes as Saurashtra took a 353-run lead.
At the draw of stumps, Unadkat was at the crease and giving him company was Dharmendrasinh Jadeja (38) at the Gandhi Memorial Science College Ground here.
For J&K, Z Sofi (3/51) and V K Dogra (3/137) were the highest wicket-taker with three wickets each, while Sameer Ali (2/111) took two and Parvez Rasool snapped one.
Brief Score:
Jammu & Kashmir 1st innings: 138
Saurashtra 1st innings: 491/9 in 122 overs (S Jackson 121; Z Sofi 3/51).