At stumps, former Royal Challengers Bangalore player J Syed Mohammed was batting on 50 scored off 142 balls with six boundaries to his credit.
He added 66 runs for the sixth wicket with former Karnataka left-hander Amit Verma (42) after Assam, who were put into bat by opposition skipper Harbhajan Singh, were left reeling at 115 for five.
Right-arm seamer Kaul took 4/81 in 26 overs while left-arm seamer Barinder Sran had 2 for 67 from 21 overs.
At the Sardar Vallabhbhai Patel Stadium, Harbhajan was spot on in opting to field after winning the toss as seven out of the eight wickets were snapped up by the medium pacers.
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Sran, who recently played one-dayers in Australia, complemented Siddharth well as he extracted some good movement off the surface.
Even third seamer Deepak Bansal (1/36 in 18 overs) kept up the pressure while bowling in tandem with his skipper as Assam could never build a partnership of significance.