SAN FRANCISCO -- The Giants announced Thursday that they've signed Drew Smyly to a one-year Major League contract, adding a veteran left-hander to help balance out the club's heavily right-handed rotation mix.

Smyly will earn a base salary of $4 million, with a $250,000 roster bonus and other potential escalators based on games started and games finished, according to Andrew Baggarly of The Athletic.

To clear a spot for Smyly on the 40-man roster, the Giants designated right-hander Trevor Oaks for assignment.

A second-round Draft pick of the Tigers in 2010, Smyly posted a 3.74 ERA over his first five Major League seasons with Detroit and Tampa Bay, but he did not pitch in '17 and '18 after undergoing Tommy John surgery. He returned to the big leagues last year with the Rangers, but he was released after posting an 8.42 ERA over 13 appearances (nine starts). Smyly later caught on with the Phillies, where he logged a 4.45 ERA over 12 starts under new Giants manager Gabe Kapler.

Smyly, 30, is the second starter signed by the Giants this offseason, joining right-hander Kevin Gausman, who agreed to a one-year, $9 million deal in December. San Francisco had been looking to improve its rotation depth from the left side, as it already had several righties, including Johnny Cueto, Jeff Samardzija, Gausman, Tyler Beede and Logan Webb, in the fold for 2020.

Tyler Anderson, who was claimed off waivers from the Rockies and is coming off knee surgery, is likely the only other lefty in the mix for a starting job this spring, which could boost Smyly's chances of cracking the Opening Day rotation.

The moves for Smyly and Gausman mirror the Giants' additions of Derek Holland and Drew Pomeranz on one-year deals last year. Holland and Pomeranz opened the 2019 season in the rotation, though they were both moved to the bullpen after struggling as starters. Pomeranz quickly rebuilt his value as a reliever and was dealt to the Brewers at the Trade Deadline for Mauricio Dubón, who will enter Spring Training as the favorite to win the starting job at second base.