FORT MYERS, Fla. -- Nathan Eovaldi possesses a lightning bolt of a right arm, and that was apparent by the back-to-back fastballs at 100 mph that he fired to Nelson Cruz in the bottom of the second inning of Monday's 3-2 loss against the Twins.

But the heat that Eovaldi unleashed in his first start of Spring Training was not the most significant development.

What was much bigger to Eovaldi was the return of an old friend that abandoned him too many times last season -- the splitter.

For Eovaldi to be what he was two years ago when he helped the Red Sox win the World Series, he needs his secondary pitches to prevent hitters from sitting on his elite heat.

And no pitch does that better than his splitter. Right?

“Yeah, I’d say my splitter for sure,” Eovaldi said. “Last year it was real inconsistent. That was one of the pitches I really focused on this offseason. Make sure I got that back on track. Today they were really consistent.”

In two strong innings, Eovaldi gave up two hits (only one left the infield), walked none and struck out four. He cited the splitter as the catalyst to his strong Grapefruit League debut

Eovaldi especially likes to unleash the splitter on lefties, and he got several swings and misses on it Monday.

“The lefties, throw good cutters in, and speed them up, and then the splitter away,” he said.

"Oh, gosh, that's what we talk about when Nate's got his command. He's really tough to hit," said interim manager Ron Roenicke. "He had everything working."

Whether the outs come by fastballs, splitters, sliders or curves, Eovaldi is a hugely important member of the 2020 Red Sox.

“He’s huge because we need to keep our starting pitchers healthy, out on the field,” said Roenicke. “When you’re always trying to go grab guys from your Minor Leagues to come up or fill in from your bullpen to try to fill starting spots, you can only do that for so long.”

With David Price off to the Dodgers -- not to mention the star-studded, five-tool skillset that Mookie Betts possesses -- Boston needs its returning starting pitchers to come through.

It starts with ace Chris Sale and ultra-talented lefty Eduardo Rodriguez. But third in line is Eovaldi, who took turns being injured and inconsistent last season.

As it turns out, those two things were inter-related.

“I think a lot of the inconsistency comes from the injury,” Roenicke said. “I think with Nate, you get him on a roll. Health-wise, he looks great so far. It starts with that great stuff. He starts to get command with it, then all of a sudden you have this great pitcher. I know he’s got great stuff.”

The key will be for Eovaldi to locate his great stuff.

“These big league hitters are getting better and better and getting more used to seeing that type of velocity, even up to 100,” Roenicke said. “When you miss even with 100, it still gets hit at times. The more velocity we see in this game, the more they get used to it, you’re going to have to really start making pitches like anybody.”

Though Eovaldi will never admit it, the workload he endured during that memorable October of 2018 must have taken its toll last year.

Who could forget Eovaldi pitching late into the night and early into the morning for six innings of heroic relief in Game 3 of the World Series, which ended in the 18th inning when Max Muncy walked off with a homer for the only win of the series for the Dodgers.

Even in defeat, Eovaldi was widely credited with making Boston’s eventual World Series victory possible because he saved the rest of the bullpen. In fact, he roved from the rotation to the bullpen throughout the playoffs. But for someone who has endured arm injuries over the years, the after-effects couldn’t help but be felt in 2019.

“Physically I feel really good,” Eovaldi said. “This offseason I worked a lot on my kinetic chain and posture. Coming into Spring Training, I feel like it’s helped out a lot. I know this was the first outing but so far I’ve been really good.”

And if Eovaldi can stay there throughout the season, the Red Sox will have a big weapon.

“If he’s healthy, he’s a big arm,” said Red Sox slugger J.D. Martinez. “You saw him out there today, he’s throwing 100 miles an hour. It never hurts when you have a guy like that in your rotation. If he’s healthy and he goes out there and stays healthy, he’s going to be a big piece.”