Suranjoy, a Commonwealth Games gold-medallist and Asian Games bronze-medallist, beat Shin Dongmyung of Korea 16-14 in a high-voltage encounter.
The 19-year-old Sumit, in contrast, outpunched Luong Van Toan of Vietnam 14-2. Toan is a gold-medallist from the South East Asian Games last year.
Suranjoy will now face off against Mongolia's Tugstsogt Nyambayar, who was his nemesis in both the 2009 and 2011 World Championships. Sumit will square off against Kim Hyeongkyu of Korea in his next bout.
"Suranjoy had a very tough bout as the Korean guy is also a tempo boxer. He really stretched Suranjoy in the last three minutes," national coach Gurbax Singh Sandhu told PTI from Astana.
"He has a tough opponent in the next round as well and we are keeping our fingers crossed. Sumit, on the other hand, made it completely one-sided, it was an easy one for him," he added.
