Siddikur shot a clinical two-under-70 in the final round to keep the trophy in the host nation of Bangladesh. He ended the Rs. 40 lakh event with a remarkable 16-under-272 total.
Kumar finished runner-up at 10-under-278 after his impressive final round of four-under-68. It turned out to be the Lucknow golfer's career-best finish.
Siddikur (69-66-67-70), the overnight leader by seven strokes, drove home the advantage on the final day with considerable ease as none of the other golfers posed any threat to his lead.
The 32-year-old Rahman was three-under through 11 holes on Saturday after chipping-in for birdie on the fifth and also setting up tap-in birdies on the 10th and 11th with a couple of top-class chip shots.
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The two-time Asian Tour winner made another chip-in on the 16th, his second of the round and fifth of the week, to cruise home despite the bogeys on the 12th and 17th.
"My chipping was the best aspect of my game this week. I made five chip-ins through the tournament. I didn't leave myself too many long putts, especially on the last day. I felt I kept up the intensity through the final round and was therefore in total control," said Siddikur.
The 25-year-old Sanjeev's career-best finish and second top-10 of the season also propelled him from 12th to sixth position in the PGTI Order of Merit.
Sanjeev said, "I'm delighted with this result. I've been playing really well since last year and the results are gradually getting better for me."
Delhi's Shamim Khan (70) finished third at eight-under-280. He continues to lead the PGTI Order of Merit.