When star slugger J.D. Martinez signed a five-year contract with the Red Sox during Spring Training in 2018, the pact included the uniqueness of three opt-out clauses -- following the second, third and fourth years.

Those opt-outs proved to be unnecessary. Martinez informed the Red Sox on Sunday, hours before the 5 p.m. ET deadline to elect free agency, that he is opting back in for the third straight year.

Martinez, who had a strong bounce-back year in 2021, is set to earn $19.375 million in the final season of his contract.

“You learn over time in this game not to be too surprised by anything. Certainly happy he’s [back] with us,” said Red Sox chief baseball officer Chaim Bloom. “He’s such a force in the lineup, not only what he produces but how he transforms what the lineup looks like around him and how he changes the conversation in the cage, the preparation before games. So we’re very excited he’s back with us.”

In addition, the Red Sox exercised their $7 million club option on starting catcher Christian Vázquez, who has played 614 games in his career -- all of them for Boston.

The Sox declined club options on right-hander Garrett Richards and left-hander Martín Pérez, as both those pitchers -- who started the season in the rotation and ended it in the bullpen -- are free agents.

The option on Richards was for $10 million and included a $1.5 million buyout. Pérez’s option was for $6 million and had a buyout of $500,000.

The most significant decision of the day for the Red Sox was the one made by Martinez. They can now go about their offseason knowing that a key part of their offense is under contract for another season.

It remains to be seen how the return of Martinez will impact Boston’s pursuit of free agent Kyle Schwarber, who became an instant fit with the Red Sox after he was acquired at the Trade Deadline. Schwarber recently declined his portion of a mutual option worth $11.5 million.

While manager Alex Cora was able to fit both sluggers in the lineup down the stretch by using Schwarber in left field, at first base and at designated hitter -- rotating Martinez between DH and the outfield -- that alignment might not be as sustainable for a full season. There could also be payroll considerations.

Bloom, however, kept open the possibility of re-signing Schwarber.

“We’ve been engaged with Kyle. We’re going to stay engaged,” Bloom said. “Knowing J.D. is here changes how we look at the lineup and position-player group generally. But as I said after the season, we played some of our best baseball with both of those guys. They both fit. This just gives us more clarity going forward and which paths we take as we reshape and put together this position-player group for 2022.”

The Red Sox also have Bobby Dalbec, who smashed 25 homers in his rookie season, as part of the equation at first base. First baseman Triston Casas, the team’s No. 2 hitting prospect, could also be ready to play in the Majors at some point in 2022.

There was some speculation that Martinez would opt out this time around given the possibility that the National League will add the designated hitter for the 2022 season.

But Martinez chose the security of another season with the Red Sox, the team he has said many times that he enjoys playing for and that he helped guide to a World Series championship in 2018.

“I don’t know that there’s any outcome that would have surprised us, but we’re really glad he decided to stay,” Bloom said.

Following a disappointing performance in the abbreviated 2020 season, Martinez got off to a red-hot start in ’21. After a midseason dip, he returned to form. The 34-year-old slugger posted a .286/.349/.518 slash line (.867 OPS), while racking up 28 homers, 99 RBIs and an MLB-leading 42 doubles. Martinez was also voted an All-Star for the third time in the last four seasons (there was no Midsummer Classic in '20).

In the 2021 postseason, Martinez was one of the most productive players for a Boston squad that advanced to Game 6 of the American League Championship Series, slashing .344/.447/.688 with three homers and 10 RBIs.

Though Vázquez had a disappointing season offensively, hitting .258 with six homers and 49 RBIs in 458 at-bats, the Red Sox feel the 31-year-old has enough to offer on both sides of the ball to justify bringing him back at such a reasonable price.

Vázquez’s best season was 2019, when he belted 23 homers to go with 72 RBIs and a .798 OPS. He followed with an .801 OPS in ’20.

Despite his struggles in 2021, Vázquez had some key hits, most notably his walk-off homer in the bottom of the 13th inning in Game 3 of the American League Division Series against the Rays.

As for Richards, the 33-year-old righty went 7-8 with a 4.87 ERA in 40 appearances (22 starts) with the Red Sox last season. Pérez also went 7-8 in 2021, posting a 4.74 ERA in 36 outings (22 starts).