India, playing Afghanistan in Tests for the first time since hosting the visitors in their first-ever Test in 2018, won the toss and opted to bat at the New PCA Stadium in New Chandigarh on Saturday.
The match came after a quick turnaround for many of India's players from their IPL campaigns.
India's openers struggled for fluency in the first session and Rahul was handed a major reprieve in the 11th over when a clear edge went unreviewed by the visitors.
Replays later confirmed Rahul would have been dismissed, and the 34-year-old made the most of his lifeline, combining for a 139-run partnership with Sai Sudharsan after opener Yashasvi Jaiswal was dismissed by Mohammad Saleem for 24.
That partnership ended when Saleem took his second wicket, dismissing Sudharsan for 81 with a delivery that carried through to wicketkeeper Afsar Zazai.
Rahul then featured in a 67-run third-wicket partnership with captain Gill, who contributed 39 runs and helped see his teammate to a 12th Test century off 165 balls.
However, Rahul was dismissed off the very next ball by Ziaur Rahman, caught at extra cover, finishing on exactly 100 runs for his third Test century in a row.
"I'm really happy that I could get some time in the middle. To make that switch from T20 to Test cricket in a matter of a couple of days was the most pleasing thing," Rahul said.
"It was extremely hot, I was exhausted ... I had to make that switch of letting the ball go and getting used to the conditions.
"Sometimes you sit and over-analyse. I try to not restrict my shots. I played a few more shots in the morning than I would usually do, but it didn't frustrate me."
Gill (103no) soldiered on alongside Rishabh Pant (50no) and the pair kept their foot on the gas to take India past the 350-run mark, before the India captain reached his 11th Test century right before the end of play.
The match is a chance for India to build some confidence ahead of series against Sri Lanka and New Zealand this year, after a difficult couple of years in Test cricket that have included losses to the Kiwis, South Africa and Australia.
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