BOSTON — Rick Porcello’s Red Sox story has been a tale of two pitchers.

The 27-year-old sinkerballer entered 2015, his first year in Boston, with lofty expectations after signing an $82.5 million contract extension just before the season began. It’s not unfair to say he didn’t quite reach them during the first four months of baseball.

His ERA ballooned to 6.08 on July 1 after his worst start of the year — seven earned runs in just two innings pitched in a Canada Day shellacking against the Toronto Blue Jays. It settled at 5.81 on July 29 after another two-inning outing in which he gave up six runs (five earned) to the Chicago White Sox before hitting the disabled list for a month.

But when he returned in August, he was a different pitcher, finishing the year 4-4 with a 3.14 ERA in his final eight starts, never pitching fewer than six innings.

That success has continued into this season, where entering Tuesday’s start against the San Francisco Giants he owns an 11-2 record and a 3.66 ERA. He’s undefeated (8-0) at Fenway Park in 2016, too.

Farrell wouldn’t say for certain that the DL stint really made the difference. Instead, there’s been one simple adjustment that has made all the difference for Porcello, who relies on a sinking movement in his two-seam fastball to induce ground ball outs.

“You can more readily point to him re-establishing his sinker. That’s his trademark pitch. That’s the one he’s willing to drive with,” Farrell explained. “I think there was — pre-DL last year — there was maybe the intent to pitch with a little bit more velocity, causing him to be up in the strike zone a little bit. So he went to his two-seamer a little bit, he was more mid-thigh (in terms of pitch location) rather than knee or below. So the location of the two-seamer, I think, has been the direct link to his consistency.”

After returning from injury, Porcello suddenly had much better command.

“I think he’s done a great job of limiting the number of baserunners that are in his control — in other words, he’s cutting down his walk rate,” Farrell elaborated. “I think those two things combined have allowed him to be as consistent as he’s been”

If the numbers are any indication, Farrell is spot on: Before last season’s All-Star break, Porcello’s walks per nine innings pitched (BB/9) was a whopping 2.06, ranked 157th in baseball. He finished the year 21st overall, and currently is sixth in baseball this season at 1.67 BB/9.

Clearly it’s made quite an impact.

“The biggest adjustment is that after he’s thrown consecutive four-seamers, he’s been able to get back to quality location with his two-seamer,” Farrell added, “whereas last year, pre-DL, that wasn’t the case. … It’s been the location of his two-seamer that’s been the biggest difference.”

A win Tuesday makes him the first Red Sox pitcher to start 9-0 at Fenway Park since Hall of Famer Dennis Eckersley did so in 1978. A Red Sox victory would make him the first Sox pitcher to earn a win in his first 10 home starts since Curt Schilling in 2004.

In other words, what Porcello has changed is working.

Thumbnail photo via Bob DeChiara/USA TODAY Sports Images