In a must-win contest for both, young Chadha slipped up after leading 3-1 before getting back into groove and chalk out a 26-17, 25-37, 50-36, 40-3, 11-47, 6-44, 36-25 win in an all-Maharashtra Group G contest.
Rehman fought back well under pressure to force the decider before going down fighting in a tight final frame in the best-of-seven tie.
In another exciting tie, India junior snooker champion Laxman Rawat of Delhi sneaked into the knock out round despite losing 3-4 to J Varun Kumar of Tamil Nadu in Group N on better frame aggregate that pushed his vanquisher out.
Trailing 0-2, Rawat recovered to win three frames in a row that proved decisive in sealing his place in the next phase at the cost of Kumar. Former Maharashtra no. 1 Nikhil Ootam topped the group.
Defending champion Shahbaz Khan of PSPB, Maharashtra snooker champion Hasan Badami, India sub junior snooker no. 1 Dhwaj Haria of Gujarat, Lucky Vatnani of AP, Mahesh Jagdale of Maharashtra, Yogesh Sharma of Maharashtra, Rafath Habib of Railways and Devendra Joshi of PSPB also entered the last 32.
Missing out were last year's runner-up Kamal Chawla of MP, Manan Chandra of PSPB, India junior snooker no. 3 Lalrina Renthlei of Mizoram and Ashok Shandilya of Railways.
Among the women, national 8-Ball champion Neena Praveen of Tamil Nadu enjoyed a clean slate with three wins to qualify for the quarter-finals from Group B, along with junior and sub junior national snooker champion Varsha Sanjeev of Karnataka.
Umadevi Nagaraj of Karnataka matched Praveen
