Bajaj, who was one-under at the turn, found five birdies on the back-nine, including four in a row from the 14th to 17th hole, shares the lead with American Dino A Giacomazzi.
Thailand's Atthaphon Sriboonkaew ignited his Tour card quest with a flawless five-under 66 and was tied third alongside Australian Steven Jefferess, who matched his efforts.
The 2010 Asian Games team silver-medallist as an amateur, Bajaj is making his second attempt at the Qualifying School. He nailed four straight birdies in his closing five holes on a day disrupted by a lengthy suspension due to inclement weather.
There are 14 Indians in the final stage of the Asian Tour Q-School. The Final Stage features 243 players from over 30 different countries and will be played over five rounds (90 holes) across two courses.
All Final Stage entrants will play two rounds before the field is cut to the leading 140 players and ties, who will then play another two rounds.
After 72 holes, the field will be cut to the leading 70 players and ties who will then proceed to the fifth and final round held only at the Rayong Green Valley Country Club.
At the conclusion of 90 holes, the top 35 players and ties will be ranked accordingly for the 2018 season.
1. Rahul Bajaj (65); T-45. M Dharma (70); T-69 Himmat Rai (71); T-98 Honey Baisoya, Manu Gandas and Karandeep Kochar (72 each); T-120. Deepinder Kullar, Angad Cheema, Viraj Madappa and Divyanshu Bajaj (73 each); T-154 Samarth Dwivedi and Udayan Mane (74); T-188 Veer Ahlawat and Gaurav Pratap Singh (75 each).