The Estonian announced last month that she would be retiring after the grass-court Grand Slam in London at the tender age of 27.
She said on social media that she had been told by medical specialists that she had lumbar disc degeneration in her back.
Kontaveit beat Italian qualifier Lucrezia Stefanini (25) 6-4, 6-4 on Wednesday to prolong her farewell tournament and will play Czech 32nd seed Marie Bouzkova (24) in the second round.
"It definitely is emotional, and yeah, it feels a little different," she said after her win.
"But really excited that I get to play a few more matches here hopefully, and just do my best every time I walk on the court, and that's what I have been doing my whole career. Really want to do that for the one last time."
Kontaveit, who rose to a career-high ranking of number two last year but has now slipped to 81 in the world, said a number of players had tried to persuade her to prolong her career.
But she insisted that she could not go on.
"It's really sweet that they're trying," she said. "A lot of people tried, I think.
"But, I mean, these decisions, because I cannot play without pain pretty much the whole match, so it was something that of course I considered for a very long time.
"But it was a very difficult decision and once I decide something big like this, I don't usually start doubting it."
Kontaveit said she found out about the problem with her back last year and tried different approaches including core-strengthening exercises and resting.
"It just took a few matches to start feeling it again, very short matches, as well," said the Estonian, who took painkillers to get through her opening match on Wednesday.
"I feel like I tried everything I could."
Kontaveit, whose best result at a Grand Slam event so far has been her run to the quarter-finals of the 2020 Australian Open, said she would continue her psychology studies after quitting the game.
"I really enjoy studying and I really am very interested in psychology so hopefully in the future as I learn more and more about it, it's going to help me more and more," she said.
