The South Korean began the day with a three-shot lead but was caught on the back nine before retaking top spot on his own with a birdie on the 16th.
A bogey on the next dropped him into the play-off at 16 under but after taking a brave line over the back of the green on the first visit back up the 18th, he got up and down for a winning birdie.
The win for Wang comes in just his 29th European Tour event and at 21 years and 144 days old, he is the third youngest player to win three events after Matteo Manassero and Seve Ballesteros.
It was heartbreak for South African Van Zyl, who looked the favourite when he got on the green in two on the play-off hole but a second three-putt of the day cost him dear as he finished runner-up on the European Tour for the fifth time in his 150th event.
Swede Lagergren is also searching for his first win and he left himself too much work to do when he pulled his second shot in the play-off into the greenside bunker.
Wang won the Sir Henry Cotton Rookie of the Year award last season after his victories at the Trophée Hassan II – also after a play-off – and the AfrAsia Bank Mauritius Open and could now climb as high as 39th in the Official World Golf Ranking and earn a potential invite to the Masters Tournament.
“When I was young, I really wanted to play the Masters,” he said. “I always imagined that I would play there. Maybe now I have a chance to play the Masters. So I’m so happy about it and I hope I’m going to get in the Masters. That’s my dream, dream tournament.
“This feels really fantastic for me. It’s really, really great. I’m so happy.
“I just don’t want to get any pressure this year. I just want to learn from the other players. I just want to keep winning, I hope. I’ve really got a lot of confidence right now, I just want to play another tournament.
I’m so happy about it and I hope I’m going to get in the Masters. That’s my dream, dream tournament – Jeunghun Wang
“I was really nervous on the back nine. I missed a lot of greens but my chipping was really good today so I saved everything and finally I won.
“I just wanted to try to make birdie at the last. I didn’t think about anything. I just wanted to try to make birdie.”
Wang and Van Zyl both got off to blistering starts with birdies on the first and second and when Van Zyl added further gains on the third and fifth, the lead had been cut to one shot.
A bogey on the next after a three-putt bogey meant that Wang turned with a two-shot lead but a run of 11 pars allowed the rest of the field to close in.
Frenchman Mike Lorenzo-Vera was the first player to catch him as he made birdies on the first, third, sixth, seventh, 11th, 12th and 13th and, despite a bogey on the 15th after finding the water, he rolled in an eagle putt from the fringe of the drivable 16th.