On the mound, Justin Slaten’s sophomore season is off to a stellar start. He hasn’t yielded an earned run in eight of nine appearances, and entered Sunday having retired his last 18 batters.

Behind the scenes, however, the affable Red Sox right-hander has been navigating the painful loss of his grandfather, who passed away early in spring training. They’d been on Slaten’s baseball journey together; his grandfather even built out his own spreadsheets to predict his draft outcome and track his stats.

“It’s been tough,” Slaten told the Herald on Sunday. “For as long as I can remember, every time I pitched, good or bad, the first thing I would see on my phone when I came inside was a text from him. It’s been weird not seeing that now.

“I think about it often,” he continued. “Like, the game that I had in Baltimore, I would have come inside and he probably would have been like, ‘Hey, they got lucky,’ make an excuse for me or be like ‘You gotta shake that one off.’ And then when I have good games, ‘You got to be better.’”

Opening the season visiting the Texas Rangers was especially bittersweet for Slaten. It was supposed to be a special family occasion for the East Texas native, who spent his entire professional career in the Rangers organization before the New York Mets selected him in the Rule 5 draft and dealt him to the Red Sox last offseason.

“Getting a save there in the first game of the season was kind of emotional,” he said. “When he was really sick, he had never seen me play professionally and he was really going to try and make that series, and obviously wasn’t able to.”

“My dad was saying, ‘It’s so weird, as soon as you got that out, I pulled out my phone to text Dad,’” Slaten recalled. “It’s been hard, and I think about him every single day when I’m pitching and when I get done with games, and even the other days, I think about him a lot. But also I’m super thankful for the relationship that we had.”

No one can ever take his grandfather’s place, but Slaten’s father is keeping the texting tradition alive; he’s taken to sending his son postgame messages, often quoting his grandfather.

And in fellow reliever Greg Weissert, Slaten has found a best friend who dishes out a similar combination of tough love, honesty, and support.

“We both can be self-deprecating, and we’re the first people to tell each other, like if I throw a pitch and it sucks, he’ll be like, ‘That was bad.’ And I’ll do the same thing,” Slaten explained. “But if I have a bad game and I’m feeling bad about myself, he’s going to come into the clubhouse and be like, ‘They just got lucky.’

“Nobody’s in there making excuses (for themselves), but we try to help ease each other by making excuses for (each other). He would never let me make an excuse for one of my bad outings, I would never let him make an excuse, but I’ll make one for him.”

“We like to keep things very lighthearted and have fun, but also we’re very honest with each other.” Slaten said. “This game is way too hard and we have way too long a season to take it super serious all the time.”

The lightheartedness was evident as Weissert, sitting down the dugout bench during this interview, described Slaten as the Ernie to his Bert. Slaten concurred that they “do everything together” like the Sesame Street duo, but countered that Weissert is more Oscar the Grouch.

“We are so stupid, it’s crazy that they’re paying us to play this game,” Slaten joked.

Slaten is approaching his second season with the same mindset he had as a rookie: earn it every day.

“I think last year something that really worked for me was just keeping the mentality of like, every single day trying to prove that I belong, and I’m still trying to do that,” he said. “Every time the (bullpen) phone rings and they tell me that I’m in the game, this switch kind of flips in my head and I’m out there like, ‘You got to go out there and you got to earn this, you know, to earn this job.’

“I think that’s something that’s really worked to my benefit, making sure that I don’t take a single day, a single game for granted up here, because, I’ve said it before, it could end tomorrow and I would be grateful for the stuff I have, but I don’t want it to end tomorrow. I want to play this game for as long as I can.”

Red Sox injury updates

The Red Sox expect to activate right-hander Brayan Bello for Tuesday night’s series opener against the Seattle Mariners, manager Alex Cora announced Sunday morning.

Lucas Giolito went five innings in his rehab start for Double-A Portland on Sunday, giving up three earned runs on six hits (including a home run), striking out four, with zero walks. He threw 65 pitches, 47 for strikes. He entered the contest having allowed four runs on nine hits, nine strikeouts, and seven walks in his previous three rehab starts (7.2 innings). Before Sunday’s outing, Cora said the right-hander will “probably” have another rehab outing before being activated.

Richard Fitts (right pectoral strain) played catch on Sunday, and catcher Connor Wong (pinky fracture) is already hitting off a tee.

Kutter Crawford (right knee) is expected to go to Fort Myers at the end of the week to begin pitching in extended spring training games.