BOSTON -- Cole Ragans keeps one-upping himself.

Last week, the Royals’ lefty set a career high in strikeouts with eight against the Mets. On Monday, he surpassed that mark with 11 against the Red Sox, allowing just two runs (one earned) in a career-high 6 2/3 innings in the Royals’ 6-2 walk-off loss at Fenway Park.

The disputed call that led to Monday’s rough ending for the Royals shouldn’t override what Ragans did for the majority of the series opener. The Royals were eager to get another look at the 25-year-old starter after the Trade Deadline last week, and now he’s fully solidified his spot in the rotation after the Royals acquired him in the deal that sent Aroldis Chapman to the Rangers in June.

In three starts with the Royals since then, Ragans has a 1.02 ERA (two earned runs in 17 2/3 innings) with just 15 hits allowed, four walks and 22 strikeouts.

“That kid was really, really good,” Red Sox manager Alex Cora said. “Wow. We talk about the Trade Deadline and what teams do and don’t do, whatever. But to get an arm like that to their program, where they’re at, that’s A-plus. We’ve seen a lot of good pitching the whole season, and the ability to throw 98, 99 with a good changeup, cutter … Stuff-wise, one of the best that we’ve seen.”

While Boston starter Brayan Bello quieted the Royals until the seventh inning, when they were able to string three consecutive two-out hits to tie the game, Ragans carved up the Red Sox lineup with a good mix of all five of his pitches.

He worked around one walk and two hard-hit doubles, which led to the lone earned run against Ragans in the fifth. The other run was unearned in the third due to catcher Freddy Fermin’s throwing error.

Ragans relied on his slider again, the pitch he added when he was traded to the Royals as a weapon against lefties, and registered four whiffs on 10 swings with it. He fooled hitters with his changeup, getting nine whiffs on 13 swings with the pitch, and curveball, which landed for six called strikes.

His cutter looked better because of the situations he used it in -- something he’s been trying to improve since joining Kansas City. Lefties have historically hammered that pitch, but Ragans used it strategically against them Monday; with two outs in the fourth, Ragans threw a cutter to Triston Casas, who grounded it to first base to end the inning.

“Something a little smaller than the slider, so if I did get it down and away, I was trying to get a ground ball or something, get them out in front and get them off the heater a little bit,” Ragans said. “Where the slider is more [about] getting swing and miss.”

And he blew his fastball by the Red Sox, reaching up to 98.5 mph and averaging 96.5.

“Felt like everything, for the most part, was commanded in the zone pretty well,” Ragans said. “It’s a good feeling going out there knowing that this is a really good lineup but also feeling like I can throw any pitch at any given time.”

Ragans ended the sixth at 93 pitches, which could have been the end of a stellar night. But he still looked strong, so manager Matt Quatraro sent him back out for the seventh -- and Ragans added two more strikeouts to his line.

He got Casas, a lefty, to whiff on an elevated 97.4 mph fastball, then turned around and struck out Luis Urías, a righty, on an 87.2 mph slider. It ended Ragans’ outing at 104 pitches.

“Trying to get the curveball to the bottom of the zone, the slider to the bottom, the changeup,” Ragans said. “Then [having] something you can elevate and go back to those pitches definitely helps because it’s changing guys’ eyesights. That’s a really good lineup over there, so you have to mix it up well because they can do damage quick.”

Pitching at Fenway Park for the first time presents challenges for any pitcher -- especially a left-hander with the Green Monster over his shoulder.

Ragans barely batted an eye.

“I honestly think he couldn’t care less about where he’s pitching,” Quatraro said. “It’s nameless, faceless hitters in whatever ballpark. He’s got to trust his stuff, and that’s what he did tonight. Those are some of the best hitters in the game up and down that lineup. For him to go out there and just attack says a lot about him.”