SAN DIEGO -- The Mets’ good news Saturday was that right-hander Kodai Senga was added to the National League All-Star roster. But for every action there is a reaction, and the Mets faced it via Padres southpaw Blake Snell.

That, more than anything, led to San Diego snapping the Mets’ season-high six-game winning streak with a 3-1 decision Saturday night at Petco Park.

• Game Story: Alvarez rips 17th homer ▶️

When Senga was informed he was headed to the All-Star Game, that meant Snell was not. Snell was hopeful that his recent run of stellar pitching would have him headed for Seattle, near where he grew up.

So Snell was motivated, and a motivated Snell is an effective Snell. He retired the first eight batters he saw and racked up 11 strikeouts in his six scoreless innings.

“He has good stuff, and he makes good pitches and doesn’t make too many mistakes,’’ Mark Canha said. “When you have the kind of stuff that he has, the arsenal he has, and you are not making mistakes, it just makes it real tough as a hitter. The stuff moves a lot and is explosive.’’

New York’s best chance against Snell came in the sixth, when Brandon Nimmo and Tommy Pham drew one-out walks with the heart of the lineup coming up and Snell nearing the end of his stint.

But with Snell reaching the 100-pitch mark, he induced Francisco Lindor to fly out to right and then he doused the uprising when Pete Alonso grounded out to shortstop, running Snell’s scoreless innings streak to 16.

With Snell spent, the Mets showed a pulse in the seventh.

Rookie Francisco Alvarez continued his amazing run with a solo home run off reliever Luis García. It was Alvarez’s fifth homer in his last seven games and his 17th of the season -- the second-most ever by a catcher in his age-21 season.

Alvarez has gone deep in four of the five games on this road trip. And in the one he didn’t reach the seats, he went 4-for-5.

The Padres struck for three runs in the second inning off starter David Peterson. Matthew Batten delivered the big blow with a two-run blast, the first home run of his career. That frame represented Peterson’s lone hiccup in his 5 1/3 innings. He struck out seven.

“It just came down to a couple of pitches for me, and that’s on me,’’ Peterson said.

But it wasn’t the Mets' night, not in a game in which they struck out 17 times, didn’t get a hit with a runner in scoring position and saw Lindor make two errors at shortstop.

A seven-game winning streak would have been dandy heading into the series finale Sunday before the All-Star break. But winning six of seven is swell, as well, and it breathed new life into New York’s season.

The small picture is the Mets losing a game, but the bigger one reveals a once-struggling club that is riding a wave of positive vibes.

“Certainly, we are human beings and we have those feelings, just like you do when you are trying to do something a little better than you did the last time,’’ manager Buck Showalter said. “Nobody is robotic; we have feelings. You hear noise and you’re trying to stay together, and our guys have done a good job of staying together.’’

Before the gang splits up for four days, a Sunday win would add more fuel for a second-half run.

“We’re playing well, and you just want to keep that momentum going,’’ Canha said. “I think we are proud of what we have done this last week, and I think the sense of urgency is very much there. We have to keep doing it, and that continues tomorrow.’’