For the second straight year, the opening weeks of the MLB season misrepresented what was to come.

Similar to the 2018 Mets, who started red hot before losing 85 games, the Mariners appeared to be the surprise team of the league this campaign, taking 13 of their first 15 contests. A few weeks later, however, it's clear they aren't genuine contenders, with a recent slump dropping them to 21-23.

Instead, the unheralded Diamondbacks appear to be MLB's upstart team. Their 23-19 record is notable not just because of their offseason moves, which hinted at a retooling process, but also because they've played one of the most difficult schedules in baseball thus far.

Is their run sustainable?

Let's assess what's made the Diamondbacks so competitive so far, and whether they project to keep up their play for the next four-and-a-half months.

5.1 runs per game (10th), .786 OPS (5th), 106 wRC+ (8th)

The Diamondbacks have been above average on offense, even when accounting for their hitter-friendly ballpark. After trading Paul Goldschmidt and losing A.J. Pollock via free agency, that level of competency is pretty remarkable.

Arizona's lineup currently boasts six regulars who have been above league norms in terms of on-base plus slugging and wRC+ this season, though two of those players seem to be playing beyond their current abilities.

Outfielder Jarrod Dyson is riding career highs in average, on-base percentage, slugging percentage and walk rate at age 34. It's rare for someone never known for his bat - Dyson possesses a career on-base plus slugging of .668 - to discover lasting success this late in his career. So, it's unlikely the speedster will continue at this pace, though his value has always been tied to other areas, such as his defense and stolen base ability.

Another overperforming hitter is 33-year-old outfielder Adam Jones, who had declined to about league average at the plate in his final three seasons with the Orioles. Jones now has a career-high walk rate and has launched eight home runs in just 40 games, fueling the second-best slugging percentage of his career. Unlike Dyson, Jones carries the long-term track record of being a great hitter, and it's possible his change of scenery and place on a winning team has helped him find a groove.

Outside of Dyson and Jones, it's difficult to poke holes in Arizona's order.

David Peralta (.914 OPS) remains an underrated stud. Eduardo Escobar (.894 OPS) is showing signs that his breakthrough 2018 was not a fluke. Christian Walker (.943 OPS) is hitting the ball as hard as anyone in baseball, ranking in the 98th percentile in average exit velocity, according to Statcast. Ketel Marte (.825 OPS) has built on a quietly excellent campaign last year to deliver power and a well-rounded plate approach.

Plus, third baseman Jake Lamb is expected to return from injury in June. He hit 29 home runs in 2016 and 30 in 2017. At 28, there's reason to think he can be a strong contributor following his insertion into the lineup.

It's noteworthy, however, that the Diamondbacks do not have a single top-100 hitting prospect, according to MLB.com, and no significant minor-league hitter in their system ready for big-league promotion in 2019. John Sickels of The Athletic takes a similarly grim view, ranking just two Diamondbacks hitters in his league-wide top 100 and projecting neither of those players to reach MLB this year.

As a result, Arizona does not have much organizational depth from which to bolster its squad midseason, and it would likely need a deal on the trade market to improve its offense in the case of additional injury or widespread regression. The front office might be hesitant to be aggressive given a contention timeline originally geared beyond 2019.

That leaves the Diamondbacks locked into a lineup able to provide consistent run support if all goes right, but at risk of slipping in the second half of the campaign if injuries strike or overperformers nosedive.

4.64 runs allowed per game, 4.25 ERA (12th), 4.18 FIP (14th)

What was supposed to be Arizona's strength entering the campaign has held up reasonably well to this point, surviving a tough home environment to limit damage. The rotation has been excellent, sporting a 3.99 ERA, but the bullpen ranks eighth-worst in baseball at 4.67.