ST. PETERSBURG -- Shane McClanahan’s start couldn’t have begun much worse. Two pitches, two swings, two hits and a run on the board for the Red Sox. Seven pitches later, he’d allowed  another run on two more singles to right field.

“That's just kind of how baseball is. Sometimes you're going to get beat,” McClanahan said. “Just got to keep attacking. Don't change anything.”

• Box score

And by the time he walked off the mound, finally done for the day, McClanahan couldn’t have done much more for the Rays. The left-hander breezed through seven innings, allowed only two hits after the first inning, struck out seven batters without walking anybody and earned his first win of the season in Tampa Bay’s 5-2 victory over Boston on Sunday at Tropicana Field, the Rays’ fourth win in five games.

McClanahan’s line was impressive enough. So is the fact that he became the first Rays starter to record a win this season and remained the Major League leader in strikeouts, with 31.

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But when you consider the way he dismantled the Red Sox lineup, and the context of his outing, it’s even more apparent that the 24-year-old lefty has taken the leap from talented young pitcher to front-line starter in his second season.

“There's probably not many big league pitchers out there who have taken bigger steps forward than what he has,” said Kevin Kiermaier, who made an outstanding over-the-shoulder basket catch behind McClanahan in the sixth. “As he gets older and more experience and more confidence, the better he's going to get -- and that's scary.”

Take it from the Red Sox, who had to play a convoluted guessing game against McClanahan’s four-pitch arsenal. Last season, he put together an impressive stretch while leaning mostly on his fastball and slider. In his last three starts, his curveball was his most effective secondary offering. On Sunday, he used his changeup to neutralize a heavily right-handed lineup.

Boston’s hitters whiffed on 21 of their 52 swings and went down swinging on each of McClanahan’s strikeouts. Five came on the changeup, by far his least-used pitch a year ago and one that barely factored into his profile as a prospect. But he threw his changeup 23 times, and the Red Sox missed nine of the 15 times they swung at it.

“He did a good job keeping us off-balance,” Red Sox hitting coach Pete Fatse said. “I think that’s kind of a strength of his going into this year. He was pitching a lot off his fastball and slider last year, and going more curveball-changeup this year is an effective mix for him. It’s been so far this year.”

With elite stuff and trust in Tampa Bay’s defense, McClanahan has no fear of pounding the strike zone with all four pitches. His seven innings tied for the longest start of his career and the longest for any Rays pitcher since he went seven last Aug. 7, and he threw only 86 pitches. Another way to look at it: He faced 27 batters and threw only 22 balls.

“When he fills up strikes, he’s going to get deep in ballgames and give us a chance to win a lot of games,” Rays manager Kevin Cash said. “His stuff is kind of second to none.”

With McClanahan flying through the innings, no relievers even warmed up until the sixth. But lefty Brooks Raley sat down just as quickly as he got up when McClanahan proved he wasn’t bothered by the flash of neck stiffness that briefly drew Cash and head athletic trainer Joe Benge out of the dugout.

Colin Poche warmed up in the seventh and pitched the eighth, and Ryan Thompson picked up the save in the ninth. Otherwise, the bullpen that worked so much throughout Saturday’s whole-staff no-hit bid had a hard-earned day off.

“I didn't want the bullpen to come in at all. They've been busting their butts all season for us,” McClanahan said, smiling. “A lot of pitchers [worked] yesterday, so I didn't really think I had the luxury today of maybe not having my best stuff or my best outing.”

He arguably had both, and he received the run support he needed near the end of his start. Shut down by former teammate Rich Hill for four innings, the Rays were gifted three baserunners by Red Sox reliever Phillips Valdez in the fifth -- hit batter, walk, hit batter -- and sent up pinch-hitter Ji-Man Choi to face righty reliever Ryan Brasier with one out.

Choi launched a two-run double off the left-field wall to tie the game, then Yandy Díaz scored on Manuel Margot’s groundout to put the Rays ahead. Kiermaier tacked on a run by scoring on a wild pitch in the sixth, with Randy Arozarena thrown out at the plate on the same wacky play. Then Díaz added on in the seventh with his first homer of the season.

It was Choi’s hit that stood out the most, as he has reached in 12 of 13 pinch-hit plate appearances -- with three doubles, one homer and 11 RBIs -- since the start of last season. Díaz said the Rays believe Choi is going to get a hit “100 percent of the time” off the bench. McClanahan had a similar idea.

“Just pinch-hit him every game. Why not?” McClanahan said. “He'd be the best hitter alive.”