SAN DIEGO — Rick Porcello spent hours in the video room and on the bullpen mound at Fenway Park last season, analyzing every mistake he made, every home run he allowed, and seeking potential fixes. Nothing he tried worked. Nothing helped him get better. Everything he tried just made it worse.

Only after Porcello spent three weeks on the disabled list with what the team announced as inflammation in his triceps did he find himself again. The seven scoreless innings he threw in Chicago in his first start back marked a turning point. The nearly 250 innings he has pitched in the year-plus since have seen him compile a 3.21 ERA.

It wasn’t a matter of throwing a harder fastball or a sharper curveball. It was a matter of mental peace.

“All I know is when I took the mound in Chicago after I came off the DL, I felt completely relaxed,” said Porcello, who will start Friday night when the Red Sox open a three-game series in Toronto. “That time off, it reset me mentally, and that was really all I needed.”

The pressure to win in Boston requires the Red Sox to spend on the game’s most talented players, as they’ve done year after year. Almost without fail, at least for a time, those players have succumbed to the pressure to live up to those lavish contracts, and not all have come out the other side intact.

How to help those players through what can be overwhelming psychological hurdles remains a challenge.

“What makes teams willing to make an investment in the individual player is they’re high-character, they’re aware of themselves and they’re conscientious,” Manager John Farrell said. “I don’t know that there’s a player with those attributes that would come into a new situation and not want to uphold his end of the bargain. That causes a particular person to try to do a little bit more and, as we know in this game, more is not necessarily better.”

“Instead of being relaxed and staying within your game and being in control, it pushes you to put more pressure on yourself,” Porcello said. “It’s really hard to play when you do that.”

Porcello has pitched himself in contention for the AL Cy Young Award. He’s unrecognizable from the pitcher who carried a 5.81 ERA into late July in his first season in Boston.

A parade of similarly high-priced free agents and trade acquisitions have underperformed upon initial introduction to Boston before and after Porcello.

David Price seemed to need the first six weeks of this season to settle in and “take the chip on my shoulder and use it the right way,” he said recently. Hanley Ramirez endured his worst season a year ago, his first year with the Red Sox. Pablo Sandoval did as well.

Carl Crawford disintegrated as an impact player after signing a $142 million contract in Boston. John Lackey chafed at the scrutiny. Not until his second season in Boston did Josh Beckett blossom into a Cy Young contender, much like Porcello. Of the team’s high-priced acquisitions, perhaps only J.D. Drew, so even-keeled as to be oblivious, never seemed to let outside pressure affect him.

“The psychology of sports is quite subtle,” said Adam Naylor, a professor of sports psychology at Boston University. “It’s not that you’re stressed or you’re not. If you’ve got just a little extra stress, your pitches aren’t going to dance like they should.”

Just getting to the majors requires tremendous mental fortitude. The expectation that comes with a mind-boggling paycheck tests that fortitude further, especially if that paycheck comes from a new team and new fan base.

A player earning $20 million like Porcello, or $30 million like Price, can come to believe any struggle is unacceptable, an impossible standard to meet. Anything less than dominance can create doubts that spiral into disaster.

“All athletes need to know how to struggle well,” Naylor said. “Part of you is like, ‘Why am I struggling when I’m talented?’ No, you’re struggling because you’re a professional athlete and it’s really tough.”

Porcello heard about it. Oh, did he hear about it. Fans made their displeasure known last season in every possible way. The $82.5 million contract he signed on the first day of his first season in Boston only provided more ammunition.

“There wasn’t any holding back on people letting me know how (terrible) I was,” he said.

Boston fans might not be more passionate as those in New York or Chicago, two significantly larger media markets. But Boston offers less competition for the spotlight than those markets, which makes for perhaps the most intense, pressure-packed environment in baseball.

“It’s not just fans showing up to the game,” Porcello said. “They’re into it as part of their daily lives. They know everything that’s going on with the team. You don’t experience that in other places. It’s just not as intense.”

“That was the most aggressive sports market that I’ve ever been part of,” said Tampa Bay Rays Manager Kevin Cash, who won a World Series ring as a catcher with the Red Sox. “I spent some brief time in New York and I still think Boston holds the crown in that regard.”

In hindsight, it only seems obvious that Porcello needed to get away, to get a bit of a fresh start. Three weeks on the disabled list represented that fresh start for Porcello, just as an offseason away from the game represented that deep breath for Beckett and Ramirez after their first seasons in Boston.

“Once you empty, you can see what’s in front of you,” Naylor said. “If you don’t empty, your body can’t join in and your mind can’t see the problem clearly.”

For Porcello and the Red Sox, that deep breath yielded one of the best pitchers in baseball.

Porcello didn’t need to work harder or care more. If anything, he needed to work a little less and care a little less, getting himself into the right frame of mind to let his talent take over.