Padres manager Bud Black made the announcement Saturday.
San Diego opens the season on April 6 at the Los Angeles Dodgers. Shields has never pitched at Dodger Stadium.
Shields signed a $75 million, four-year deal with the Padres last month. The 33-year-old righty became a free agent after pitching for Kansas City in the World Series last October.
This will be Shields' seventh season opening assignment. He pitched the last two for the Royals and did it four times with Tampa Bay.
Shields is 1-1 with a 3.31 ERA in five spring training starts. He labored through 95 pitches in 4 1-3 innings on Friday against Colorado Rockies.