NEW YORK -- What a difference a year can make.

Not only has the Yankees' exhaustive, unenviable list of injuries been a change from last season, but the Red Sox overall haven't been the same team that ended 2018 hoisting the championship trophy. Slow offensive starts and pitching inadequacies have the defending World Series champions more than a half-dozen games behind a surprising, mostly patchwork group of Yankees in the AL East race.

This weekend, the teams meet for a second time this season (New York swept an early two-game series in the Bronx). As they square off in a four-game set at Yankee Stadium, we look at what has defined each of their seasons to this point.

1. The Red Sox rotation is waking up

After a 17-2 start last year, the champs struggled out of the gate this season; Boston didn't go over .500 in 2019 until May 10. Ace Chris Sale was particularly rough, with a ghastly 0-5 record and a 6.30 ERA in his first six starts. The injury bug struck the starting rotation when Nathan Eovaldi went on the injured list and underwent surgeries to remove loose bodies from his right elbow. Lefty David Price spent a short stint on the IL, too, with elbow tendinitis.

But those early-season rotation concerns seem to be fading into the background. Since April 14, Red Sox starters have posted a 3.44 ERA, the fifth-best mark in baseball. Sale has a 2.23 ERA in May, and Rick Porcello has sported a 2.91 ERA over his past seven starts. The Sox are also striking out a lot of hitters, setting down 9.5 batters per nine innings this month, good for the fifth-best mark in the majors. -- Joon Lee

2. Pinstripe production is coming from unexpected places

No Aaron Judge. No Didi Gregorius. No Giancarlo Stanton. No Miguel Andujar. No Luis Severino. No Dellin Betances. If we'd known at the onset of spring training that the Yankees would be missing a large collection of their stars for virtually all of the first half, it would have been hard to envision them winning a division title this season. Yet here they are, currently leading the AL East with the core of an All-Star team languishing on their 14-man injured list.

Because of what they've been missing throughout the year, the No. 1 storyline surrounding these stunningly strong Yankees is the production they've gotten from a bevy of unexpected heroes. From Gio Urshela's clutch hitting and smooth defending at third base to Domingo German's savvy ace-like pitching to Thairo Estrada's steady, consistent play, the Yankees have benefited from performances few saw coming.

Eighteen players have spent time on the Yankees' IL this year, and, since the final days of spring training, the team has called up 14 players from Triple-A and pulled off three trades to stay afloat. -- Coley Harvey

3. Devers and Chavis are breaking through in Boston

When Rafael Devers reached the majors two years ago, it was natural to wonder what the Red Sox ultimately would do with 2014 first-round pick -- and fellow third baseman -- Michael Chavis. Losing Dustin Pedroia to the IL for the third straight season this year, the answer became clear: Just have them mash in the same lineup by moving Chavis over to second base. Through the first two months of the season, Devers (2.0) and Chavis (1.2) rank third and fifth among Red Sox position players in wins above replacement.

Devers, who's more than a full year younger than Chavis, came into the season facing increased expectations. Assistant hitting coach Andy Barkett said the third baseman was pressing through the first month of the season while trying to match the hype, but has since settled in, hitting .360/.393/.640 with seven homers in 100 at-bats in the month of May.

Chavis, meanwhile, has become the everyday second baseman, occasionally hitting leadoff in manager Alex Cora's lineup. When the Red Sox struggled to put runs together through much of May, the 23-year-old provided a jolt, smashing 10 homers in 33 games while hitting .280/.379/.536. He's also the clubhouse runaway leader in dropping "Dude" during news conferences with reporters. -- Lee

4. Yankees keep making all the right moves

Including players who have been called up or sent down multiple times, the Yankees have made nearly 40 transactions since acquiring outfielder Mike Tauchman on the penultimate day of spring training. It has been a dizzying set of roster moves. But based upon the way this team has played amid all of them, they've clearly been the right ones.

As much as Tauchman's acquisition in a trade with Colorado for prized young southpaw Phillip Diehl raised eyebrows in late March, it paid off. Tauchman isn't currently with the big league club, but he gave the Yankees just enough outfield depth -- with his occasional power -- through the first month of the season. And even while the .204-hitting Tyler Wade added little at the plate while he was on the major league roster, his speed contributed to a few timely runs in wins that helped spark the Yankees. Since Wade scored a ninth-inning, eventual game-winning run April 24 in Anaheim, the Yankees are 22-9.

One of the savviest moves the Yankees made early this season came during that same series in Anaheim. With a few late-night calls on the East Coast after Clint Frazier was forced to make a brief IL stint with an ankle injury, general manager Brian Cashman worked out a deal with Cleveland that brought Cameron Maybin to New York. Grateful for a chance to be back in the big leagues, and happy about finally playing in pinstripes at Yankee Stadium -- site of his first career homer -- the 32-year-old Maybin has taken full advantage. Through 27 games, he is batting .282 with a .386 on-base percentage, 12 runs scored and one memorable home-run robbery.

There has seldom been a peep made about Aaron Boone's in-game management this season. He has brought in pinch hitters in situations where he might not have a year ago. Instead of giving Gleyber Torres and Gary Sanchez full days off last Thursday in Baltimore, for example, he had both of them come off the bench with two outs in the ninth inning. The duo sparked a rally that ultimately led to a Yankees win. And then there's the bullpen: Boone has more expertly navigated pitching changes than he did in his rookie season as skipper. His relievers lead all bullpens with 10.67 strikeouts per nine innings. -- Harvey

5. Boston's bullpen remains a question mark

Complaining about the state of the bullpen is an easy thing to do, especially when considering how fickle relievers can be. When Boston let Craig Kimbrel sit in free agency this offseason, questions arose about whether the team would go out and find a closer or name one of the current relievers the man to finish off games. Instead, the team has done neither. Five relievers -- Ryan Brasier (six saves), Matt Barnes (three saves), Heath Hembree, Brandon Workman and Marcus Walden (one save apiece) -- have finished off wins for Boston this season, and Cora has not shown any indications the team will deviate from that plan in the near future.

The relieving crew has been a strong group collectively this season, striking out 10.22 batters per nine innings (fourth in MLB) while leaving 76.3 percent of runners on base, good for sixth in the majors. But the team ranks fifth in the American League in blown saves with eight. If the Red Sox really wanted to sign Kimbrel, a deal would have been worked out by now; the former Boston closer awaits the 2019 draft, when he will no longer be tied to draft pick compensation. Boston could add a relieving piece at the deadline, and the Yankees series could serve as a barometer for whether this relief crew can work through the rigors and stakes of October baseball. -- Lee

6. The schedule has helped the battered Bombers

The Yankees' schedule has been quite favorable in the early going. The moves they've made and the production they've gotten while going through their injury storm have been key, but a comparatively smooth path while riding out the storm has helped.

Entering Wednesday's series finale victory against San Diego, the Yankees had the third-most favorable strength of schedule in the majors. Their opponents had a combined .479 winning percentage. Only the White Sox and A's have had it easier.

Through their first 55 games, the Yankees have played 36 times against teams that currently have sub-.500 records. The whopping dozen games they've played against lowly Baltimore helps tip that scale, as do the seven they've already had against last-place Kansas City. Despite some early struggles against the Orioles, Tigers and White Sox at the very beginning of the season, the Yankees have gone 26-10 in games against some of baseball's worst teams. -- Harvey

7. This weekend: The momentum is on New York's side ... for now

We might have to wait until next month in London to get the sort of division-defining battle we saw between the teams at times last year. Although the Red Sox have shown glimpses of late that they might be awakening from their early-season slumber, they do still trail the Yankees by a hefty margin. Plus, beginning with their last series against the Red Sox, the Bronx Bombers have won 16 of their past 21 games at Yankee Stadium, and each of their last nine series (of at least three games) there. Expect them to add to that total. -- Harvey

This series and beyond, it'll be exciting to watch all of the new major contributors factor into the rivalry. For Boston, Chavis will get his first glimpse of the Yankee Stadium spotlight. The Red Sox bullpen will face another test in the Yankees lineup, and, along with the Astros series, this could serve as a measuring stick for the state of the relief corps. Between Torres and Frazier, the Yankees are bringing a lot of emerging power to the table. The intensity in the rivalry hasn't come close to the astronomical highs of 2003 and 2004, and might not for a long time. But the rivalry continues to evolve, especially with a new generation of stars leading the way. -- Lee