Nearly 17,000 tickets sold out within minutes for the two-game opener at Gocheok Sky Dome where the Dodgers defeated the San Diego Padres 5-2.
Roger Aranda, 49, said he flew from California with his son to cheer for Ohtani and the Dodgers.
"My favourite player is Mookie Betts, now I'm becoming a big fan for Ohtani," he told Reuters, wearing a blue Dodgers jersey and a hat. "I hope our Dodgers win. I want to see a victory here today."
Drew Jackse, 26, travelled from San Diego and said he just wanted to see a game of baseball.
"The Dodgers are a good team, but we're good too," he said. "It's going to be a very tough game but yeah, it's going to be exciting to see what it's like on the inside."
Fans erupted in thunderous ovation when the Dodgers scored four runs in the eighth inning to turn a 2-1 deficit into a 5-2 lead, with key shortstop Mookie Betts delivering an RBI single to left field, followed by an Ohtani single that plated another run.
The Japanese-born two-way star, who is limited to batting this season following elbow surgery, went 2 for 5 with a stolen base in his Dodgers debut since signing a 10-year, $700 million contract in December.
South Korea's baseball league is famous for its concert-like cheering culture, with fans singing personalised songs and making dance moves for each batter alongside cheerleaders, who introduced fight songs for all Dodgers and Padres hitters.
"The energy the enthusiasm from the Korean fans is great," Dodgers manager Dave Roberts told a press conference after the game. "It was a nice collection, combined effort from the Korean fans and our own home cooking."
Dodgers starter Tyler Glasnow, who gave up two runs, two hits and four walks over five innings while throwing 77 pitches, said it was a "really cool, super unique" experience.
"You can kind of tell everyone's locked into the game," he said.
US Ambassador Philip Goldberg shared photos of him watching the game with Rahm Emanuel, the US ambassador to Japan, on social media platform X saying it was great to celebrate "our shared love of baseball together."
Hours earlier, police investigated a bomb threat but no sign of an explosive device had been detected, a security official at the stadium said.
The threat, written in English, was sent in an email to an official at South Korea's consulate general in Vancouver, Canada, and said the sender was a Japanese lawyer, the Yonhap news agency said.
Officials at the Seoul Metropolitan Police Agency and Guro Police Station in the district where the stadium is located did not immediately confirm the report or could not be reached for comment.
When asked about the bomb threat, Padres manager Mike Shildt said it was "unfortunate" news but he had "full confidence" in security authorities.
Kim Myeong-seo, a 33-year-old Dodgers fan from the southeastern South Korean city of Daegu, was not concerned about the bomb threat.
"I have no worries as our country has very strict security," he said. "It was very difficult to get a ticket ... I'm just so excited and want to go in as soon as possible."
