World Cup winners India slump to Zimbabwe loss in first T20
The hosts struggled to 115 for nine after being sent in to bat at the Harare Sports Club, with leg-spin and googly bowler Ravi Bishnoi taking a career-best four for 13.
But India, fielding a youthful team that did not include any of the side that won the World Cup in Barbados last Saturday, were bowled out for 102 in reply.
The loss ended a streak of 12 successive T20I wins by India.
"We bowled pretty well but we let ourselves down in the field. Everyone looked a bit rusty," said Gill at the post-match presentation.
"We spoke about taking time and enjoying our batting but it didn't pan out that way."
India lost their first four wickets for 22 runs inside the first four overs, with new caps Abhishek Sharma (0) and Riyan Parag (2) among the failures.
It became 43 for five when Dhruv Jarel was caught at cover and India's hopes effectively ended when Gill was sixth out, bowled by opposite number Sikander Raza hitting across the line for 31 with the total on 47.
"It would have been best for us if I stayed to the end," said Gill. "I was very disappointed with the way I got out."
Off-spinner Raza, who took three for 25 and was named man of the match, said he was happy with the win but disappointed about his team's batting.
"This isn't a wicket where you get bowled out for 115. Credit to the bowlers of both sides but clearly an indication we need to up our skills. Our catching and ground fielding was amazing."
In a low-scoring match, an unbeaten last wicket stand of 25 between Zimbabwe wicketkeeper Clive Madande (29 not out) and Tendai Chatara, who faced nine balls but did not score a run, proved crucial.
Chatara then played a key role with his fast bowling, taking three for 16, including two of the four wickets that fell in the first five overs of India's innings.
Washington Sundar gave India hope after they lost their ninth wicket with the total on 86.
Sundar, who earlier took two for 11 in four overs of off-spin bowling, made 27 before he was last man out.