English began the day co-leading with Ryan Palmer, but he found himself trailing as he made the turn with Niemann in the midst of a 9-under 64 performance.
After making four birdies through Nos. 11-15 to match Niemann at 25-under, English gave a stroke back on the 16th and went to the final tee needing a birdie to force a playoff. He hit a beautiful approach into the final par 5 but couldn't convert his short eagle putt for the win.
In the playoff, English made birdie while Niemann's second shot into the par 5 left him with a tricky up-and-down he failed to pull off.
The win marks the 31-year-old's third career PGA Tour title and first since 2013.
"It feels amazing," English said after his victory. "All the hard work that has gone into this, all the highs and lows of golf that it brings over a career. And I feel like I've gotten out of my valley and getting back to the tournaments and some of the quality of golf that I know I can play."
English, who was exempt into the field by qualifying for the 2020 Tour Championship after last year's unique schedule, climbs to No. 17 in the world with his win in Kapalua, Hawaii. He ranked as low as No. 369 in August 2019.
Here's how the leaderboard finished at the 2021 opener:
|Place||Player||To Par||R4 Score|
*Denotes playoff winner.