There were some tense moments in both sets, with Hercog cutting a 4-1 deficit to 4-3 in the first set and jumping out to a 2-0 lead in the second set, but the No.1-seeded Radwanska never really looked like she was in any serious trouble, running out a 6-3, 6-3 winner in an hour and 15 minutes.
Radwanska is going for a career-first in Seoul this week - she has never successfully defended a WTA title. The furthest she has gone was reaching the final the next year - she did that at Tokyo [Pan Pacific], winning the title in 2011 and finishing runner-up in 2012 (losing to Nadia Petrova).
"The first match is always tricky," Radwanska said. "For my first match here I think it was a good one. I didn't start well in the second set, but I'm happy I could win it in straight sets anyway.
"I'm really happy to be here again and I will try my best to defend my title."
Radwanska was asked about the fans in Seoul. "Even though the stadium wasn't full today, it felt like it because they always cheer so loudly and enthusiastically here," the World No.5 said.
"It's always nice to hear their support here. We have great fans in Seoul."
Awaiting Radwanska in the second round is Chanelle Scheepers, who won her first round match on Monday. Radwanska leads Scheepers in their head-to-head, 3-0, but the matches haven't been easy.
The other seeds in action during the day had mixed results, with No.2 seed Karolina Pliskova, No.3 seed Klara Koukalova and No.6 seed Kaia Kanepi all moving through, but No.8 seed Heather Watson falling to American qualifier Nicole Gibbs, 7-5, 6-2. Watson originally led 5-3 in the first set.
Among the unseeded winners was Maria Kirilenko, the 2008 champion here and a wildcard into the draw this year as she continues her comeback from a knee injury that put her out the first three months of the season. The Russian battled past WTA Rising Star Donna Vekic in three sets, 3-6, 6-2, 6-4.
"It was a tough time after my injury last year. I haven't played much this year and after Wimbledon it got worse so I couldn't play much of the summer either," Kirilenko said. "I really missed playing and I'm happy I could win this match today, because it was my first long match so far this year.
"Donna has a good serve and she's a powerful girl - it was a really tough match."
Won my favorite 3 sets match! ?Let's go! pic.twitter.com/lttBCGzz6F