NEW YORK -- Before the swing, there was the smirk.

It was the top of the ninth inning on Aug. 13 at Yankee Stadium. The Boston Red Sox were trailing 2-1, down to their final two outs. Hanley Ramirez had just struck out on three pitches from Aroldis Chapman -- 101, 102 and 103 mph, according to the scoreboard radar reading. And now, the youngest player in the majors stepped in against the hardest-throwing pitcher in what seemed to all the world like a classic mismatch.

The bat never left Rafael Devers' left shoulder as the first pitch zoomed in at 103 mph. The kid -- 20 years old and nicknamed "Carita," loosely translated in English as "baby face" -- shuffled his feet and took two small steps back. Then he smiled, ever so slightly, as though he had seen all he needed to see.

Three pitches later, Chapman cranked it up again to 102.8 mph, and Devers did what 301 left-handed hitters before him hadn't done. He took Chapman deep on a two-strike pitch.

Game tied. Crowd stunned. Momentum shifted.

Of the two best teams in the American League East, the Yankees were supposed to be the one led by rookies. Aaron Judge redefined the standard by which all future first-year players are measured with his otherworldly first half. Gary Sanchez, not technically a rookie after collecting 229 plate appearances last season, is nevertheless in his first full major league season.

And for much of the season's first half, Judge, Sanchez and the rest of the Baby Bombers -- 23-year-old ace Luis Severino and 24-year-old rookie lefty Jordan Montgomery, in particular -- had the Yankees in first place. A season supposed to be about rebuilding instead was about contending, a year ahead of schedule.

But the Baby Bombers were upstaged in August by the Baby Bosox. While Judge slumped badly, piling up strikeouts at a historic rate, Devers and rookie left fielder Andrew Benintendi enabled the Red Sox to win four of six games between the teams and stretch their lead in the division from a half-game on Aug. 1 to 5 1/2 games entering play Thursday.

With young stars Mookie Betts, Xander Bogaerts and Jackie Bradley Jr. struggling to find consistency, Benintendi has been Boston's most valuable player since the All-Star break, according to Fangraphs' WAR. Devers, meanwhile, is batting .294 with eight homers and a .900 OPS, production that surpasses what veteran third baseman Todd Frazier has done (.217, five homers, .716 OPS) since the Yankees were more aggressive than the Red Sox in pursuing him at the trade deadline.

"[Devers] is a young kid that seems like he is enjoying playing baseball," Cleveland Indians manager Terry Francona says. "He's just seeing it and hitting it, and he's whacking it and it doesn't seem to matter who's pitching. Whether it's Chapman, he's using the whole ballpark and hitting the ball with authority. You’ve got a really good young hitter kind of in that zone right now.

"And Benintendi, it’s one of the prettiest swings you’ll ever see."

The Yankees have seen enough of it.

Like Judge, Benintendi retained his rookie status despite getting called up last August. He struggled so much through the middle of the season that manager John Farrell began sitting him against left-handed pitchers. In the midst of a 13-for-78, 20-strikeout funk, Benintendi was benched on July 31 and Aug. 1.

He began heating up before the Red Sox arrived in the Bronx on Aug. 11, and with most of his extended family in attendance at Yankee Stadium, he went on a tear, going 5-for-13 with three home runs and nine RBIs in the three-game series. He finished off the weekend by notching the go-ahead single in the 10th inning of the game Devers tied against Chapman.

Benintendi's surge has coincided with Judge's swoon. In general, Judge hasn't hit since the All-Star break. Against the Red Sox, he has been as invisible as a 6-foot-7, 282-pound man can get. The Sox attacked him with high fastballs, and he went 1-for-18 with six strikeouts in a four-game series at Fenway Park coming out of the break and 2-for-22 with 11 strikeouts in six games this month.

The gap has narrowed in the Rookie of the Year race, but it's probably too late to swing the voting completely. Judge's first half -- he had 30 homers and a 1.139 OPS at the All-Star break -- was simply too historic to be overcome even by Benintendi, the spring-training favorite to win the award.

"I think he's experienced some of the things we expected," Farrell says of Benintendi. "There was going to be some ebbs and flows in there, some stretches where there was going to be some frustration emerge. But as we turn into this month, he's carried us to a certain extent. I just love the way he, for the most part, is a very even-keeled person and even-keeled player."

The same can be said for Devers, whose heart rate seems to remain unchanged regardless of the situation.

Devers got only 35 at-bats in Triple-A before the Red Sox called him up July 23 in a move that appeared to be premature. After months of speculation that Frazier would wind up in Boston, the Yankees completed a trade on July 19 that brought Frazier and relievers David Robertson and Tommy Kahnle from the Chicago White Sox.

At the time, Red Sox officials were only hoping that Devers could provide a similar burst of energy to Benintendi a year ago. But with Betts, Bogaerts and Ramirez scuffling, Devers stepped into the middle of the order and produced more than even his biggest supporters within the organization expected.

Carlos Febles, Devers' manager at Double-A Portland, raved about his ability to hit the ball the opposite way to left field and make contact with two strikes, skills that have been on display all month.

The league is already changing the way it attacks Devers. Despite going 2-for-3 in Wednesday night's series finale in Toronto, he is only 7-for-42 with 12 strikeouts in his past 11 games.

"The book travels quick," Farrell says. "All of a sudden he's getting pounded in with some fastballs, some cutters. The biggest thing is for Rafael to understand how the adjusted attack plan against him has taken place."

There are signs Devers gets it, including his double last Sunday against hard-throwing Baltimore Orioles reliever Mychal Givens. His regression is also a reminder, though, that the Red Sox will need more down the stretch from Betts, Bogaerts and Ramirez.

But as the AL East rivals brace for one final showdown in New York, the fact that the Red Sox are in control of the division is a testament to how well the Baby Bosox have played.