The 42-year-old Colsaerts, who's also been a Ryder Cup vice-captain with the European team, likened the DLF Golf and Country Club course in New Delhi to a major championship layout as he recovered from two over after three holes with the aid of five birdies in his last 11 holes on Thursday.
"The rough is high this year, the greens are firmer and it's a little bit like a mini US Open, it's a really hard course," said Colsaerts, who was a member of the winning 2012 team.
"I would like to stay as patient as I was today and keep understanding that the pars are good, if you make a few birdies it's great. Everybody's going to make bogeys and I'm going to try to keep the ball in play as much as possible."
Armitage continued his trend for making fast starts, carding seven birdies and three bogeys in his round.
It is the third time this season Armitage has found himself in such a position after day one, the 37-year-old having carded an opening 63 in the Ras Al Khaimah Championship and a 65 in last week's Singapore Classic.
Armitage, who won his sole European Tour title to date in the European Open in 2021, will be hoping it is a case of third time lucky in India after finishing second in Ras Al Khaimah and fifth in Singapore.
"I really like the golf course, it's different, you've got to play some great golf to shoot a good score and I putted fantastic today so it's really cool to get some success around here," Armitage said.
The leading Australian was Jason Scrivener, who shot a level-par 72, while Austin Bautista and Daniel Gale were both four over after 76s.
After a good week at the Singapore Open which he finished with a top-20 place, Melbourne's Cameron John had a bit of a nightmare with his opening-round 83, which included a quintuple-bogey 10 at the long eighth hole.
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