Earlier in the day, Jang teamed up with Lim Jong-hoon for the men's doubles gold medal. On Saturday, Jang and North Korean player Cha Hyo-sim combined for the mixed doubles title.
Jang is the first player in the Korea Open's 18-year history to win three gold medals in one event. The mixed doubles was contested at this tournament for the first time this year.
"I still can't believe I've won three titles here," Jang said after clinching the men's singles gold medal. "I guess it will sink in after some time passes. I've gained so much confidence at this event, and I feel like I've taken a big step forward. I am happy to be playing table tennis."
With the men's singles title at stake in the tournament finale, world No. 30 Jang had little trouble against the 103rd-ranked Liang.
Up 4-1 in the first game, Jang continued to pick up points with an array of winners and strong returns. In the second game, the two players were deadlocked at 8-8, before Liang's back-to-back unforced errors allowed Jang to go up 10-8. He closed out that game 11-9.
The South Korean remained in control in the third game. Then up 4-2 in the fourth game, Jang reeled off five unanswered points for a convincing 9-2 advantage, and then closed out Liang 11-3 for the game and the match.
In the men's doubles final Sunday, Jang and Lim beat Ho Kwan Kit and Wong Chun Ting of Hong Kong 3-1 (11-8, 19-17, 9-11, 11-9).
Jang and Lim opened a 4-1 lead in the first game before closing it out 11-8. In the second game, they led 10-9 before allowing Ho and Wong to force deuce. At 17-17, the South Koreans got two straight points on unforced errors by the Hong Kong team and Lim's powerful drive.
They led 9-7 in the third game, two points away from the gold medal, but conceded four unanswered points as the match moved to the fourth game.
In the deciding game, Jang and Lim clung to a 10-9 lead, and closed the deal thanks to the opposition's miscue on match point.
Jang and Lim will go at it again at this year's Asian Games, set from Aug. 18-Sept. 2 in Jakarta and Palembang, Indonesia.
Jang, who will only compete in the men's doubles in Indonesia, said, "We'll try to stay grounded and keep working hard to achieve great results at the Asian Games." (Yonhap)