Veteran boxer Mary Kom reached the semi-finals of the women's fly (48-51kg) category, assuring India a medal in the event at the 17th Asian Games here Sunday.The 31-year-old Indian beat Si Haijuan of China 3-0 to win by a unanimous decision.The Chinese fighter gave Mary Kom a stiff fight but the Indian showed her class and made her punches count.The judges gave 39-37 scores in all three rounds in favour of Mary Kom.A semi-final berth means Mary Kom has assured India of a minimum bronze and a possible silver or gold if she makes it to the final.The Indian boxer will take on Vietnam's Le Thi Bang in the semis Tuesday.