Britain's Raducanu, the 2021 US Open winner and eighth seed in Seoul, came back from 1-3 down in both sets to beat Jaqueline Cristian of Romania 6-3, 6-4.
The first-round match was originally scheduled for Tuesday but was pushed back by heavy rain in the South Korean capital.
"It hasn't been easy, I feel like I've played this match for the last three days," Raducanu said afterwards.
Raducanu next plays Czech Krejcikova, who won the 2021 French Open and last year's Wimbledon crown.
Top seed and six-time major champion Iga Swiatek faces Romania's Sorana Cirstea on Thursday as the Pole gets her title bid underway.