"The protest has been rejected. The reasons were not given to us but in cases like these, it is extremely rare that a protest is accepted and the decision overturned," national coach Gurbax Singh Sandhu said.
Sumit lost 14-15 to Florentino in a closely-contested bout which left the Indian team and Sports Minister Ajay Maken enraged, prompting a quick protest.
Sangwan found himself on the wrong side of the judges' scoring pattern as the boxer, despite dominating the second and third rounds, did not get enough points for his efforts.
"Sumit is fine now. Obviously, he was very upset with the result. But there is no other option but to accept things and move on. He will have his chances in future," said Sandhu about the 19-year-old from Haryana.
Indian Boxing Federation Secretary General and acting Chef-de-Mission Muralidharan Raja had stated that the protest was specific to the scoring in the second round.
"The protest was specific to round two. We thought Sangwan should have got more points in that round," Raja said.
Sangwan, one of the bright youngsters on the Indian boxing scene, had made the cut for the Games after winning a gold medal in the Asian Qualifiers earlier this year.
Last night, he came into the final round trailing by two points following the first two rounds going 5-4 and 5-4 in favour of the seeded Brazilian.
His loss was a blow to the Indians, who have already seen Shiva Thapa lose in 56 kg bantamweight class.
However, 2008 Olympic bronze medallist Vijender Singh (75kg) and Jai Bhagwan (60kg) have progressed to the round of 16 and Vikas Krishan (69kg) has got a bye into the pre-quarterfinals.
Today, L Devendro Singh (49kg) and Commonwealth Games gold-medallist Manoj Kumar (64kg) will open their campaigns in the mega-event.