Somdev was severely tested by a player who was making his Davis Cup debut and ranked 289 placed below him before prevailing 7-6 (4) 7-6(3) 6-4 after three hours and thirty minutes of intense tennis in the opening singles.
The 17-year old Korean, who had ended runner-up in the Wimbledon junior championship last year, showed that he was progressing well but ultimately fell short against a player who does not give up easily.
Sanam, chosen ahead of tall and big-serving Saketh Myneni, though could not make it an all-win day for India as he lost 6-7 (5) 4-6 4-6 to Korea's number one player Lim in the second rubber, which lasted two hours and 45 minutes.
Sanam, who was originally drafted as a reserve along with Jeevan Nedunchezhiyan, got the chance to play after Yuki Bhambri pulled out of the tie due to a foot injury.
The Koreans were the underdogs to start with but they showed the visitors that tie would not be a walk in the park for them.
Today's result means that Rohan Bopanna and Saketh Myneni must win tomorrow in the doubles rubber against Hyung-Taik Lee and Sang-Woo Noh to ease off the pressure on the team.
It will be the second time that seasoned Bopanna and Myneni will play together in a Davis Cup tie.
A victory will leave India requiring only one point on the last day to secure a berth to the World Group play-offs.
