The 24-year-old made five birdies on his final seven holes on Sunday and scored a round of 66 that put him -17 and three strokes ahead of the rest of the field.
Rory McIlroy had the lead until the final lap but shot a disappointing 74 to finish sixth in a tie.
Matt Fitzpatrick fired a six-under par 66 to move up the leaderboard and jeopardize Morikawa’s spot at the top of the leaderboard, but it was only enough for second place.
Morikawa didn’t need to win this week to win the Race to Dubai, especially as his closest rival Billy Horschel finished 32nd.
But he flipped the style on the track to secure his sixth professional win.
“It feels so good. I would be lying to you if I said I wasn’t watching what Matt Fitzpatrick is doing today, and boy, did he take a run,” said Morikawa.
“It’s an honor. To put my name up against many, many greats in the Hall of Famers – that’s something special. I get touched just talking about it.
“The way my head is wired, I’m always on the lookout for what’s next. But I’ll try to enjoy this one. It’s something special, it’s the end of the year, I’ll enjoy it as best I can. “
It is the latest in an incredible run for the American over the past two years.
Morikawa also won the WGC Workday Championship earlier this year, which together with winning the Open played an important role in making him top the European Tour points list.
The only two events he played in Europe that year were the Scottish Open and then a week later at Royal St George’s, but the points offered for the majors and the WGC events meant he was that week at the DP Tour World Championship as leader of the Race to Dubai.
Morikawa also played a huge role in securing the Ryder Cup in the US, winning three and halving one of the four games he had played.