SEATTLE -- For all the Mariners’ historical success on Opening Day, the 2024 edition was largely a sleeper.

There were a few big moments, headlined by Mitch Haniger homering in his first game back and Dylan Moore making things interesting with a pinch-hit blast in the seventh. But Seattle was otherwise slowed by Boston in a 6-4 loss on Thursday night in front of a packed but chilly T-Mobile Park.

The loss snapped the Mariners’ three-game winning streak on Opening Day, and it was just their fourth since 2007.

What went right?
The promise that Haniger showed throughout spring continued with his 372-foot blast in the fourth. Making the moment sweeter was that Félix Hernández, Haniger’s teammate from 2017-19, coincidentally delivered the call while visiting the ROOT Sports booth.

Haniger ripped a 96.6 mph first-pitch sinker off Brayan Bello, who to that point was dealing, and punched it 102.1 mph over the right-field wall. Most of Haniger’s 119 career homers have been to the pull side, but Mariners staff have raved about Haniger’s pointed effort to use the entire field thanks to what he called “a deeper swing path.”

President of baseball operations Jerry Dipoto even said recently on the Mariners Radio Network that this is “the best version” of Haniger, including his All-Star year in 2018 and 39-homer season in '21.

“I’ve looked forward to this moment a lot,” Haniger said. “It's good to be back in a Mariners uniform. I love playing in front of our fans here at T-Mobile. It's a really special place to play, and I've been extremely grateful they brought me back.”

Haniger’s homer carried some sentimentality, but Moore’s was more towering. The utility man crushed a two-strike sinker from lefty Joely Rodríguez and sent it 409 feet beyond center field to make it a one-run game. Moore also had a great spring and will be used regularly against lefties, like on Thursday.

“We have more utilities than you think, even though it's kind of just me,” Moore said, “because all these guys that start can play all these different positions. So it'll be interesting to see how we roll with it. And then obviously, the things that come up during the season, how we adjust.”

What went wrong?
Luis Castillo flashed elite stuff, averaging 95.8 mph on both his fastballs, but he labored with command, limited to 13 first-pitch strikes in 23 plate appearances and just six whiffs despite five strikeouts.

“Some of the pitches didn't go where I wanted them to go,” Castillo said through an interpreter. “And those were the situations that got us. ... When something like that happens, all I can do is just keep attacking.”

“La Piedra” might’ve gone further without a few defensive hiccups behind him.

After a two-run homer to Rafael Devers, Castillo’s third run scored when Tyler O’Neill raced home on a chopping grounder to Rojas, who at third base made an athletic grab but hit O’Neill’s helmet with the throw, allowing everyone to reach. Yet O’Neill was only positioned to score after reaching on a forceout instead of a double play, when J.P. Crawford bobbled a chopper into his chest.

Later, after Castillo departed, Red Sox speedster Ceddanne Rafaela bested Dominic Canzone when racing for the rare triple to left field, then he scored standing on a shallow two-out single. Canzone’s cutoff throw to Crawford was at 76.8 mph, well below his 90.9 mph average last year.

And in the ninth, Luis Urías made a hesitant throw to first base despite having the would-be third out running just a few paces to his left, shy of third base, though that play didn’t later lead to a run.

“You've got to have that internal clock set right. ... Little plays like that, we certainly need to tighten up,” Mariners manager Scott Servais said.

What to make of it?
When Haniger was reacquired, the thought of him playing 120 games was an arbitrary target for success, given his flukey injury history and how long he was sidelined last year. That, plus lefty-hitting outfielders Canzone and Luke Raley, could create more platoons. But it seems clear that Haniger will regularly play against righties -- especially if he hits like this.

As for defense, Canzone looked improved in spring and Urías progressed from shoulder inflammation toward the end, drawing positives from Servais. But it was still hard to miss the two biggest positional question marks heading into the season after each had a notable hiccup in the opener.