While Shiva stunned Olympic bronze-medallist and top seed Dorjnyambuug Otgondalai of Mongolia in a split verdict, Sumit stormed past second seed Tajik Jakhon Qurbonov in the semifinal.
However, middleweight (75kg) top seed Vikas Krishan settled for a bronze medal after giving a walkover in the semifinal to fourth-seeded Korean Lee Dongyun.
"Vikas Krishan was not there in the weigh-in today morning, therefore his South Korean opponent walked over to the final," an Asian Boxing Confederation official told PTI.
The day, however, belonged to Shiva and Sumit, who notched up victories against more fancied rivals.
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Shiva, also a World Championships bronze-medallist, was the first to take the ring against the Mongolian, who is the reigning Asian Games champion.
The national will next be up against Uzbekistan's Elnur Abduraimov, who defeated China's Jun Shan in his semi-final bout.
Shiva, a two-time Olympian, was off to a guarded start and spent some time getting measure of his rival.
In fact, both the boxers seemed hesitant to launch the first attack in the opening three minutes.
The third round was a more evenly-matched affair with Mongolian also hitting the aggressive mode. But Shiva's sharp reflexes helped him stave off the challenge and get a favourable verdict after an exhausting contest.
This is Shiva's maiden medal-winning international performance in the lightweight division, to which he shifted last year in December.
Sumit competed in the final bout of the afternoon session and was hardly pushed by Qurbonov, who won a bronze medal in the last edition of the event.
India had won four medals at the last Asian Championships in 2015. Vikas had won the country its lone silver medal, while Shiva, L Devendro Singh (52kg) and Satish Kumar (+91kg) had settled for bronze medals.
India's last gold medal at the Asian meet had come in 2013 through Shiva, when he was competing in the bantamweight division. Prior to that M Suranjoy Singh (52kg) had won a gold medal in the 2009 edition of the Championship.