Yankees manager Aaron Boone announced the decision before Saturday night's spring training game with the Orioles.
Tanaka is replacing Severino, who will not make the start at Yankee Stadium because of right-shoulder inflammation. Severino was scratched from his first planned start of spring training Tuesday after feeling discomfort after throwing his first slider in a pregame bullpen session.
"Masa has clearly shown through his life really that he's really good in the big spot," Boone said.
Tanaka, 30, discussed what it means to start the opener after his outing Friday night against the Detroit Tigers.
"Obviously, if you're given the opportunity to pitch on that day, you want to go out and do your best," the right-hander said through an interpreter. "If you look back, I don't think I've necessarily been good on opening days. I've gotten some experience. We've gone through playoffs. So, if that situation were to arise, I can go out there and give a good performance."
Tanaka has made three previous Opening Day starts (2015-17) for the Yankees. New York lost all three games, with Tanaka charged with the loss in two.
Severino had his first Opening Day assignment in 2018.
Tanaka was 12-6 with 3.75 ERA in 27 starts last season.
CC COMING ALONG
LHP CC Sabathia threw 31 pitches in his fourth bullpen session and said afterward that his first batting practice outing is likely next. The 38-year-old had a stent inserted in December after a blockage was found in an artery from his heart, and he has had chronic right-knee problems that required several operations. Sabathia, retiring after the season, is expected to miss his first two or three regular-season starts.