The 38-year-old, who is a 2012 Olympic bronze-medallist, prevailed 4-1 against a rival who is 15 years her junior and a Pan American Games bronze-medallist.
In a bout that was exciting from start to finish, Mary Kom displayed some brilliant tactics to overcome the fight that Garcia put up.
"It has been very painful, the last couple of years, for everybody because of the pandemic and everything shut down. We are all suffering the same problem and every athlete has to train at home, but for us boxers we need a training partner," Mary Kom said in the mixed zone after her triumph.
"I am so lucky, I could set up a little gym with equipment and a bag, but the only thing missing was a sparring partner which is the most important for the eye contact and everything," she added about the challenges building up to the Games amid the COVID-19 pandemic.
If Mary Kom held back in the opening round to get a good measure of her rival, the veteran was aggression personified in the final three minutes after Garcia bagged the second round with some fierce punching of her own.
Mary Kom's trusted right hook aided her well through the bout and she also displayed a sharp mind by forcing Garcia to lunge at her, opening up the space for the Indian to land clear punches.
The youngster from Dominica had the stomach for a fight but was undone by her inability to strike clearly.
Mary Kom, a mother of four, will next be up against third-seeded Colombian
"I have all the medals in my hand. Olympic medal (bronze) from 2012,
"...what is left is the Olympic gold medal. That is what is driving me and pushing me to carry on. I am trying my best, if I am able to get it then I will be so grateful, but if not then I will still be so happy for all the medals I have won in the past," she added.
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