The winners of the two semi-finals compete for the gold medal while the losing semi-finalists are awarded a bronze each.
The Indian, a five-time World Champion, put in a dominant performance. But her style Monday was in stark contrast to her performance Sunday, when she beat Karolina Michalczuk of Poland.
In the first round, she sized her opponent and relied heavily on defensive tactics. She time and again tried to get inside of her opponent to land a punch but the Tunisian was able to keep her distance.
Both fighters did not throw many punches and the round ended 2-1 in the Indian's favour.
The second round, too, was similar as the diminutive Indian tried to keep away from her taller opponent. Relying on one-off punches, Mary Kom frustrated her opponent with her quick evasive measures.
Fighting conservatively, Mary Kom still was narrowly able to edge out her opponent 3-2.
With only a two-point lead, the Indian put the hammer down as she went for her opponent. Like in her pre-quarters bout, Mary Kom displayed her quick feet and fast hands with a flurry of combination punches.
She stepped inside her opponent, who had an advantage of height, and landed some telling blows. With the Tunisian clearly reeling under the pressure of the punches, Mary Kom went for the kill winning the round 6-1.
The fourth was a formality as the Indian conserved her energy and relied on counter-attacks. Her opponent too seemed to be out of energy, not even trying to reduce the seven-point deficit.
In the semi-final, the 29-year-old Indian, famously known as 'Magnificent Mary', faces Great Britain's Nicola Adams, who is seeded second in the tournament.
At the 2012 World Championship, Mary Kom was defeated in the quarter-finals by Nicola.
For the first time in India's history, two female athletes have won medals in the same Olympics. Saina Nehwal gave India its maiden badminton Olympic medal, a bronze, Saturday.