Host gymkhana cueist D'Souza, who beat Gujarat's Abhimanyu Gandhi in his opener, recovered from 1-2 down to edge past Rawat 3-2 in a Group B match.
D'Souza got off to a bright start with a break of 55 in the opening frame. Though Rawat replied with a 59 in the third frame to surge to a 2-1 lead, D'Souza came back strongly and caused the first upset in the elite draw.
Mehta, fresh from his stint in the World Pro Snooker Championships in Sheffield where he reached the second round, took time to get into his groove before getting past Hasan Badami 3-2 in Group A.
Mehta coasted to a comfortable 2-0 lead before Badami bounced back with a late challenge to force the decider.
Devendra Joshi, who lost his opener to Manan Chandra in Group C, bounced back with back-to-back wins while shocking India No. 3 Brijesh Damani of West Bengal and Amit Saboo of Maharashtra in matches that stretched into the decider.
Chandra survived a scare when he rallied from 0-2 to beat an impressive Pushpinder Singh of Delhi 3-2. It was qualifier Singh's second loss after going down to Damani, but he made amends with wins over qualifier Shakeel Ahmed and Saboo.
Wild cards Sourav Kothari of ONGC and two-time Asian champion Yasin Merchant delighted with century breaks.