The 2019 MLB season has already been filled with surprises. The Seattle Mariners–the preeminent “sellers” of this past offseason–have the best record in the bigs. The Red Sox, Yankees and Astros all have losing records. The Chicago Cubs lead the majors in batting average and on-base percentage, and yet have stumbled out of the gate at 1-4 due to bullpen struggles.

The beginning of each season brings with it plenty of overreactions (no, the Mariners are not actually the best team in baseball) as well as legitimate concerns (like the mountain heap of injuries incurred by the Yankees). In this regard, no team has been as fascinating as the defending champion Red Sox.

Boston could easily be 0-7 were it not for a pair of comeback victories against the Mariners and Oakland Athletics, respectively. Chris Sale's steep decline in velocity has suddenly made him appear more hittable, and the rotation has combined to give up 30 earned runs in just 32 innings of work.

In fact, the offense has not fared much better, and the Red Sox began play on April 4 with the worst run differential (-15) in baseball.

Of course, every game matters in a very top-heavy American League East, but Red Sox fans need not panic.

Yankees struggling as well

There might be more reason to worry had Boston's archnemesis–the Yankees–gotten off to a good start. After all, New York was one of the betting favorites to win the World Series this season, and had the best offseason of any team in the AL East.

However, the Yankees have struggled to get an early foothold on this season as well, losing two of three to both the Baltimore Orioles and Detroit Tigers in their opening homestand.

To make matters worse, the Yankees have already been utterly depleted by the injury bug. Shortstop Didi Gregorious underwent Tommy John surgery at the end of last season, offering an early setback up the middle.

Ace Luis Severino's status is still unknown after he was shut down with shoulder discomfort during Spring Training, and C.C. Sabathia has joined him on the injured list. Meanwhile, Dellin Betances had a right shoulder impingement and is sidelined for the time being.

Giancarlo Stantonhas already hit the IL, and Gregorious' replacement–Troy Tulowitzki–suffered a calf strain in a game against the Tigers.

In other words, the Yankees–who came into the season with such high hopes–are going to struggle just to survive April in the wake of all these injuries.

J.D. still raking

Sure, Andrew Benintendi and Mookie Betts have gotten off to slow starts. But J.D. Martinez continues to prove why he might be the best hitter in baseball.

Before play began on Thursday Martinez was hitting .357 with a pair of homers and a team-high seven RBIs, including a .500 clip with runners in scoring position.

Martinez has stayed hot basically since July of 2017. After getting traded to the Arizona Diamondbacks that summer, Martinez clubbed 29 homers and posted a 1.107 OPS before hitting .364 in Arizona's NLDS loss to the Los Angeles Dodgers.

And last year, Martinez made a legitimate Triple Crown bid. He finished first in RBIs (130) and second in both homers (43) and batting average (.330) while providing protection for Betts, Benintendi and Xander Bogaerts.

Martinez can opt out of his current contract after this season, so this may as well be a contract year for him. While the thought of losing Martinez in free agency may be terrifying for some fans, it should mean that he will continue to produce at a high level, and not fall victim to much regression.

Expected improvement from Mookie and Benny

Speaking of Betts and Benintendi, Boston's own “Killer B's” have had uncharacteristic starts.

Mookie is typically excellent even when he expands the strike zone, but he has made a lot of weak contact this year. According to Statcast, his exit velocity on batted balls was sitting at 87.4 mph (which would be a career-low), and his hard-hit percentage at a 23.1 clip.

Benintendi may be getting slightly unlucky. His hard hit percentage and exit velocity is mostly the same as it has been throughout his career, but his BABIP is just .200 and he has just one extra-base hit, to go along with an increased strikeout rate.

Both Betts and Benintendi have been fairly consistent hitters throughout their respective careers. And if Betts struggles, Benintendi is likely to see somewhat of a drop off because pitchers do not have to worry about Mookie on the base paths.

But Betts is a generational talent, and he is looking to increase his prospective value when he becomes a free agent after next season.

The Red Sox are clearly very core-dependent, but both Mookie and Benintendi can help ease a lot of doubts when they undoubtedly start to heat up.

Good signs from the bullpen

The primary narrative surrounding the Red Sox heading into 2019 was the apparent lack of bullpen depth. Boston were the favorites to re-sign closer Craig Kimbrel, but Dave Dombrowski continuously professed his faith in the arms that the team possessed.

Thus far that faith has mostly been rewarded. Both Matt Barnes and Ryan Brasier look more than capable in the role of closer, while Brian Johnson and Colten Brewer offer very different approaches in middle relief.

Johnson is more of a finesse lefty, while Brewer looks like yet another power pitcher in Boston's bullpen. If those two can continue to provide quality innings from both sides of the rubber, they instantly become more than merely depth pieces for manager Alex Cora.

Tyler Thornburg could be the key. He was tremendous for the Milwaukee Brewers in 2016 before missing all of 2017 due to thoracic outlet syndrome in his throwing syndrome.

He struggled upon returning to action in 2018, and has had mixed results in three appearances for the Red Sox this year. Given his potential as a power pitcher alongside the likes of Barnes and Brewer, Thornburg will be a pivotal player in whether Boston's bullpen becomes a strength or continues to be looked at as a weakness as the season progresses.

Positive regression

This is the phrase that Red Sox fans should remind themselves of throughout April. Last season was an anomaly in terms of the level of dominance that Boston had over the rest of the league. They were extremely unlikely to be that good again, especially due to their dependence on the core players and relative lack of offseason activity.

Still, the entire starting rotation should grow stronger as they go along–guys like Eovaldi have always been second-half pitchers anyway–and the lineup still has prolific potential, especially when Martinez continues to be a run-producing extraordinaire.

Chris Sale's absence in velocity is somewhat concerning, but Boston would not have risked signing him to such a lucrative contract had they previously known about any potential structural damage. Plus, his changeup is increasingly looking like an out pitch.

And with the bullpen turning in some good performances, there is plenty of room for optimism in Beantown.