The poor performances made more sense after he was found earlier this summer to have a partly torn rotator cuff, and now, after an extended, restorative stint on the disabled list, the old Niese appears to be back. He struck out a season-high nine batters on Friday night, and his teammates pummeled three home runs at spacious Petco Park, as the Mets sailed to a 5-2 victory over the San Diego Padres.

Niese improved to 5-6 and lowered his E.R.A. to 4.25. More important, he threw 111 pitches and felt good afterward, providing further evidence that his balky shoulder was rounding into shape.

“Something wasn’t right,” Manager Terry Collins said about Niese’s first half of the season. “This guy’s too good a pitcher.”

He added, “He’s showing you right now he’s a huge piece of this, and when he was out, we missed him.”

The Mets provided Niese ample support, making a big ballpark seem rather small.

They jumped ahead in the second inning, when Eric Young Jr.’s groundout scored Anthony Recker — a late addition to the lineup after John Buck departed on paternity leave — from third base.

Then came the surge. Marlon Byrd led off the third by bashing a high changeup beyond the center-field fence. Ike Davis crushed Kennedy’s very next pitch, a 90-miles-per-hour inside fastball, deep into the right-field seats. One inning after that, Daniel Murphy pulled a fastball, up and inside, inside the right foul pole for a two-run homer.

Davis’s home run was perhaps the most noteworthy of the three; it ended a 71-plate-appearance streak without one.

“I finally caught up to one and drove it out of the yard,” said Davis, who noted that he had been getting jammed on similar pitches these days. “Obviously it felt good. I hadn’t done that in a while.”

The runs supplied some leeway to Niese, who returned from the disabled list last Sunday, when he pitched six solid innings to earn a win.

He maintained his good form Friday, going another six innings, giving up one run, six hits and a walk.

“All game, the arm felt great,” Niese said. “They did a good job making me throw a lot of pitches. I’m fortunate enough that I was able to escape a few jams.”

He allowed his only run when Chase Headley homered to right to open the third inning. The Padres got their other run when they produced back-to-back hits off Scott Rice — who pitched a scoreless seventh — to open the eighth, cutting the Mets’ lead to 5-2.

After the home run Niese allowed, his toughest challenge was getting through the fifth after putting the first two batters aboard. But he did it unscathed, setting down Will Venable, Headley and Yonder Alonso to end the inning. It was an encouraging outcome, both on the scoreboard and from a physical standpoint.

“The only way he’s going to get back is to pitch,” Collins said about building up Niese’s arm strength. “After the fifth inning, I just thought, if he can go out there one more time, I thought it can help him down the road here. He went out and did a good job. He had to work hard.”

INSIDE PITCH

Infielder Wilmer Flores, who sprained his right ankle earlier this week, ran well before Friday’s game, and Terry Collins suggested he could be in the lineup Saturday afternoon.