ST. PETERSBURG -- While their top priority this offseason is improving their lineup, the Rays’ first significant addition was a move meant to upgrade their already-imposing starting rotation.

The Rays on Tuesday signed right-hander Zach Eflin to a three-year, $40 million contract -- the first notable strike on the free-agent pitching market this offseason.

It surpasses the five-year, $35 million contract signed by Wilson Alvarez in 1997 as the largest guaranteed contract for a free agent in franchise history. The largest average annual value given to a free agent by the Rays remains $15 million, which Charlie Morton earned during a two-year deal in 2019-20.

The Rays were expected to pursue a veteran starter to round out a rotation headlined by Tyler Glasnow, Shane McClanahan, Drew Rasmussen and Jeffrey Springs.

Eflin, who will turn 29 in April, spent seven seasons with the Phillies, going 36-45 with a 4.49 ERA in 127 games, including 115 starts. This past year, the Orlando native posted a 4.04 ERA with 65 strikeouts and only 15 walks in 75 2/3 innings over 20 outings (13 starts) for Philadelphia.

After beginning the year in the Phillies’ rotation, Eflin -- who’s dealt with chronic knee issues -- missed nearly three months last season due to a right knee injury. Without enough time to get built back up as a starter, he returned in September as a weapon out of the bullpen. The right-hander put together a 2.45 ERA with 21 strikeouts and two walks over 18 1/3 innings, including the postseason.

Eflin doesn’t have a history of missing many bats, but the sinker-heavy starter posted some intriguing numbers this year. His career-best 85.3 mph average exit velocity ranked in the Majors’ 96th percentile, and his career-low 31.1 percent hard-hit rate was inside the top 10 percentile. He also doesn’t give up free passes, averaging fewer than two walks per nine innings over the past three years.

• Statcast, advanced metrics on Eflin

Eflin also made an interesting change to his pitch mix this year, which may have intrigued the analytically minded Rays. After years of using his slider as his top secondary offering, he all but shelved that pitch in favor of his curveball. Opponents hit just .155 with a .241 slugging percentage against Eflin’s curve, which he threw 20.1 percent of the time (up from 10.8 percent in 2021) while generating a 43.5 percent whiff rate with it.

The Padres selected Eflin in the first round of the 2012 Draft (33rd overall) out of Paul J. Hagerty High School in Oviedo, Fla. He was traded to the Dodgers in December 2014 then, a day later, dealt to the Phillies for longtime Philadelphia shortstop Jimmy Rollins.

Barring a trade, this signing would solidify a strong starting five of Glasnow, McClanahan, Rasmussen, Springs and Eflin. The Rays have further depth behind that group in Luis Patiño, Yonny Chirinos, Josh Fleming and top prospect Taj Bradley.