BOSTON -- Through four innings on Friday night at Fenway Park, Nick Pivetta was cruising, backed by an explosive fastball that topped out at a season-high of 96.9 mph.

As Pivetta hopped out to the mound for the fifth, there was no reason to think anything was going to change, especially since batterymate Connor Wong had just staked him to a 1-0 lead in the bottom of the fourth with a bloop, RBI single.

Nobody could have known it at the time, but Ha-Seong Kim’s single that led off that fifth inning for the Padres had just changed the momentum of the game for good.

The latest reminder of how fleeting success can be? A stunning San Diego surge that amounted to nine straight batters reaching to open the inning and all nine of them scoring led to Pivetta and the Red Sox taking a 9-2 defeat in the opener of a three-game series.

So what exactly happened to lead to such a reversal of fortune?

“The sweeper. It didn’t perform that inning,” Red Sox manager Alex Cora said. “The 0-2 to Kim, base hit, next one, 1-0, home run. He just wasn't able to execute and everything happened so fast.”

The first five batters of the frame reached against Pivetta, including a two-run homer off the bat of Kyle Higashioka that put San Diego in front for good.

“Yeah, it was flat,” Pivetta said of his sweeper. “Higgy hit that home run on a flat sweeper. And then [Bryce Johnson], he also hit a flat sweeper for a double. And then I walked [Jurickson] Profar on it too. It was just flat. It wasn't as good as the first four innings.

“Unfortunate. But just go back to the drawing board and just try to get that pitch back to where it is. Sometimes pitches, they leave, and they come back. It's a new pitch for me, so I’m trying to figure it out.”

When Pivetta (4-5, 4.52 ERA) exited, the Red Sox were down, 2-1. He had thrown 73 pitches.

“I thought it was kind of a quick hook for him,” said Higashioka. “And then, I think we just kept the momentum going. That was good. That's something you want to try to do. When you get that momentum, you've got to capitalize on it.”

Cora didn’t dispute that his hook was quicker than normal, and he elaborated on the reason.

“I’m usually not that aggressive going in the bullpen, but with two days off [before Friday], and trying to give them a different look and not [go] with the lefty there. It was still early in the game,” said Cora.

Things simply backfired as Greg Weissert didn’t get the job done, allowing the first four batters he faced to do damage, capped by a three-run blast by Jackson Merrill, the ninth batter of the inning.

Quick hook or not, Pivetta took full accountability for the way the night went downhill.

This was the third time in Pivetta’s last four starts he didn’t make it through five innings.

“Yeah, I haven’t been doing my job. I need to pitch deeper in baseball games,” Pivetta said. “I need to get ahead of guys a little bit better. I think I only walked one guy, but they fouled off a lot of pitches today, and I didn't generate that swing and miss.”

Raffy mauls No. 17
With his mentor Xander Bogaerts looking on from the visitors' dugout, Rafael Devers provided one of the few highlights of the night for Boston, a Statcast-projected 439-foot missile to center in the sixth. For Devers, it was the third straight game he has homered.

“I saw some good takes. He was early and on time,” said Cora. “He’s seeing the ball well against lefties, against righties. He’s in one of those stretches that is going to be fun for a while, because he's on time.”

Halfway home
Friday’s loss left the Red Sox with a 43-38 record at the halfway point of the season, putting them on pace for 86 wins. This would be a sizable improvement over the 78-84 finishes of the last two seasons.

“We are where we’re at -- in the mix of making it to the playoffs,” said Cora. “We are a good baseball team that can do a lot of good things. I truly believe there's going to be meaningful games here in September.”