BOSTON – With three starters in their (so far) best-in-baseball rotation scheduled to become free agents after the season, it makes sense that the Twins would try to lock up a few of them to new contracts.

So agreeing to a four-year contract, the richest the Twins have ever handed out to a pitcher, with Pablo López wasn't a big surprise when word leaked out Monday, except for one thing: López isn't one of the pending free agents.

But he might be the best bet to be worth $73.5 million.

"We viewed Pablo as someone whose baseline performance level, as he has demonstrated with the Marlins, would comfortably place him among the top two or three pitchers on any team's staff," General Manager Thad Levine said in March after the Twins dealt reigning AL batting champion Luis Arraez for the 27-year-old López. "But at his age, and [after] examining what has made him so effective, we identified him as someone who could potentially elevate that baseline level [and] perhaps even ascend to the upper echelon of his craft."

After watching López make four starts, utilize an effective new pitch and post a 1.73 ERA, Levine, President of Baseball Operations Derek Falvey and ownership chairman Joe Pohlad backed up that opinion with cash, a major league source confirmed Monday. The agreement would cover the 2024 season, López's final one before free-agent eligibility, and three seasons of free agency, and pay an average of $18.375 million per year.

That salary doesn't even rank among the 25 most expensive for a starting pitcher, and the $73.5 million package barely does. According to salary-tracking website Spotrac, the four-year, $72 million contract that 30-year-old Taijuan Walker signed with Philadelphia last winter is the 23rd-richest deal for a current starting pitcher.

That number looks a lot larger when compared to the Twins' historic reluctance to risk tying themselves to an expensive pitcher for multiple seasons. The largest contract ever guaranteed to a pitcher is the $54 million over four years that Ervin Santana agreed to with then-GM Terry Ryan in December 2014.

Santana, 32 when he signed the contract, failed a performance-enhancing-drug test shortly before his first season with the Twins and served an 80-game suspension, but he pitched 500 innings with a 3.47 ERA over the first three seasons of the deal, making the AL All-Star team in 2017, before injuries limited him to only five starts in the contract's final year.

Under Falvey and Levine, Ryan's successors, the Twins have never guaranteed significant salaries for more than a season or two. Chris Paddack received a three-year contract, but worth only $12.5 million as he rehabs from Tommy John elbow ligament replacement surgery. At $12 million, Sonny Gray's salary is the highest for any current Twins pitcher and his contract expires at season's end, as does those of fellow pending free agents Tyler Mahle ($7.5 million for 2023) and Kenta Maeda ($3.15 million, with reachable incentives).

López has made nothing but positive impressions since joining the staff, which is reflected in their policy-breaking decision to commit to him for four seasons. Notably, the pitcher who grew up as a fan of fellow Venezuelan Johan Santana will earn $5 million more per season than the two-time AL Cy Young Award winner ever did in Minnesota.

"He looks great. He has a good combination of stuff and feel," manager Rocco Baldelli said during spring training. "He brings it all to the table. He's an extremely hard-working guy, which we've seen immediately. And no detail is bypassed."

Baldelli appointed López as his Opening Day starter, and the righthander responded to the honor by pitching 5⅓ shutout innings, giving up only two hits in Kansas City. It was the first time López had shown off his new "sweeper" pitch, a breaking ball in which he tries to impart enough spin to make the pitch break horizontally, away from righthanded batters.

The pitch, which López has thrown 21.9% of the time this season according to MLB's StatCast system, has been a great success. Batters have swung and missed half of them, and are hitting just .111 against it with a .167 slugging percentage when they make contact.

"It's really, really tough. It's probably going to play well to both sides of the plate, but it's really tough on righthanded hitters," Baldelli said on Opening Day. "We didn't bring Pablo over here and think that we were going to rework everything he did. I would call it small adjustments, and we've seen some of the benefits."

And now, and for the next four seasons, so has López.