BOSTON -- Here's the deal with Rick Porcello: More sinkers mean fewer stinkers. Got that?

Porcello should say those words before every start for the Boston Red Sox. If it helps, he should repeat them between innings, even as he stands on the mound. Thirty-three starts into his Red Sox career, it's clear Porcello is at his best when he is throwing his signature sinker more than any other pitch in his repertoire.

Through the first four months of the previous season, Porcello got away from his sinker and tried to instead lean on his four-seam fastball. He threw his sinker only 28 percent of the time to left-handed hitters and 41 percent of the time to righties, down from his career totals of 42 percent to lefties and 52 percent to righties, according to statistical data from Brooks Baseball. It was a horrible idea. He got pounded for a 5.81 ERA through 20 starts and was so bad the Red Sox placed him on the disabled list with a triceps strain and a fragile psyche.

Upon his return, Porcello increased his sinker usage to 44 percent against lefties and 58 percent against righties and posted a 3.14 ERA in eight starts. This season, he has thrown his sinker 49 percent of the time to lefties and 57 percent to righties. The results have been as good as can be.

Porcello shut out the New York Yankees in seven innings of an 8-0 rout Saturday night at Fenway Park and stretched his scoreless streak to 13 1/3 innings. He is one of three AL pitchers with a 5-0 record. The others are Detroit Tigers right-hander Jordan Zimmermann and Chicago White Sox ace lefty Chris Sale. Porcello has gone at least six innings in 13 consecutive starts, the longest such streak in the majors.

More sinkers, fewer stinkers. Can it really be that simple?

"Yes and no," pitching coach Carl Willis said. "Look, even the simple things in this game can be difficult. He had to work extremely hard to get the sink back, to get that mindset back, because he had gotten away from it a little bit. But once you get to that point, I think it's simple because it allows him to then be himself and pitch to his strengths. Nothing's simple in baseball at this level, but it's a simple concept, I guess."

We'll leave it to Willis -- and the armchair psychologists out there -- to analyze why a sinkerball pitcher would stray so far from his sinker, though the pressure to live up to being traded for slugging outfielder Yoenis Cespedes and signed to a four-year, $82.5 million contract extension before throwing his first pitch for the Red Sox is probably a good place to start.

It's clear, though, that getting back to what made him an effective mid-rotation starter with the Tigers for six seasons wasn't as simple as merely throwing more sinkers. According to Willis, throwing more four-seam fastballs caused Porcello to raise his arm slot ever so slightly. It wasn't until the final week of a lousy spring training, after reviewing video with Willis and fine-tuning his mechanics, that the 27-year-old right-hander made an adjustment that allowed his arm slot to click in.

Porcello has gotten better with each start this season. After he beat the Toronto Blue Jays in his first two starts, he gave up three runs and struck out nine batters in seven innings against the Tampa Bay Rays on April 20, and he blanked the hapless Atlanta Braves five days later. Against the punchless Yankees -- these are hardly Bronx Bombers -- Porcello got nine groundball outs, which matched his total from his previous start and was a sign his sinker was sharp.

"I think the mindset's the same: Keep the ball down, first and foremost, and everything plays off of that," Porcello said. "That's been a consistent approach since I came back from the DL last year. I'm just trying to go out there and execute that plan."

It hasn't hurt to get a few swift kicks in the rear from Christian Vazquez, the take-charge catcher who has caught Porcello's past three starts. If Porcello strays too far from his sinker, Vazquez is there to remind him.

"Porcello, when he gets Ball 1, Ball 2, he can get lost in his mind," Vazquez said. "I want to let him know that I'm here, behind him. 'Let's go, let's go.' He erases that, and he attacks the zone some more. That's very important with him -- erasing his mind and just pitch."

As long as Porcello is pitching with his sinker, that is.

"History tells us that there's possible struggles here and there that will happen," Willis said. "But I think everything he has been through, particularly last year, he has come out of it a stronger person and a stronger pitcher to deal with off-days or things that aren't working out like he wants them to. He's in a good place right now."