Bob Dutton

Bob Dutton

   SEATTLE — The biggest concern emerging this week for the Mariners isn’t their ongoing inability to match up with Houston. That was a known deficiency — although the gap seems wider than ever after losing three of four at Safeco Field.

   A bigger issue looms in a bullpen that remains spotty despite a dominant Edwin Diaz at the back end. The relief corps has a 4.59 ERA through 17 games after Thursday’s 9-2 loss to the Astros in the series finale.

   Yes, it’s early, and small sample sizes can be notoriously misleading, but the Mariners’ top three set-up relievers —Juan Nicasio, Nick Vincent and Marc Rzepczynski — all have ERAs higher than 5.00.

   For now, forget challenging Houston in the American League West race. Those bullpen numbers will torpedo any chance the Mariners have at making a legitimate run for a wild-card spot in their quest to end a 16-year postseason drought.

   Let’s reset.

   Recall that general manager Jerry Dipoto, after losing out in the Shohei Ohtani sweepstakes, made no move to bolster the rotation. Dipoto said he addressed that need last year by adding Mike Leake, Marco Gonzales and Erasmo Ramirez in the season’s second half.

   Dipoto instead supplemented what was already viewed as a solid bullpen by signing Nicasio and adding depth through a series of smaller-print moves such as Chasen Bradford, Mike Morin, Shawn Armstrong and Dario Alvarez.

   But it was deeper than that.

   The Mariners’ approach represented a step toward an emerging industry trend to rely more heavily on the bullpen. They sought to build a deep stable of arms who, to some extent, could be shuttled between the big leagues and Triple-A Tacoma.

   Last year provided the Dipoto, manager Scott Servais and the entire Baseball Operations staff  a forced (and unwelcome) blueprint when injuries devastated their rotation.

   This year, though, THIS is the plan, and it underscores another cultural shift within the game.

   It wasn’t that long ago that clubs saw 1,000 combined innings from their rotation as a benchmark. No longer. A year ago, Washington led the majors with 973 innings from its starters. The Mariners, ravaged by injuries, only managed 870 2/3.

   This is a growing trend. No club reached 1,000 innings from its rotation in 2016, and only two clubs hit that target in 2015.

   Similarly, a true staff workhorse was, until recently, someone who pitched at least 200 innings, while anything less than 180 innings prompted concern regarding a starter’s durability as well as his reliability.

   Felix Hernandez posted eight straight seasons of 200-plus innings from 2008-15 but, a year ago, only 15 starters throughout baseball logged 200 innings, and none reached 215.

   Further, only 34 pitchers made it to 180 innings in a starting role — barely one per club. Ariel Miranda led the Mariners with 158.

   That widespread decline in workload among starting pitchers is prompting debate regarding whether the 162-inning standard to qualify for the ERA title needs to be adjusted.

   Starting pitchers are now judged, increasingly, on whether they make it twice through the opposing lineup while keeping their club in the game. Being called a five-and-diver used to be a slur. Now, it’s a goal.

   That declining bar makes old-timers (and some no-so-old-timers) shudder, but the point here isn’t to dismiss the new standards. Doing so is pointless since they stem from from analytics, the bloodless science that increasingly rules the game.

   There are those who still rage against defensive shifts, but the numbers conform those shifts work far more often than they don’t. So, they’re not going away. Neither is the trend toward a higher reliance on the bullpen.

   No, the point here for the Mariners is much simpler. 

   In an era when bullpens are more important than ever, their relief corps is underperforming. Sure, we’re barely 10 percent into the season. And, yes, it could turn around. Fact is, though, it needs to turn around. Because right now, the Mariners’ bullpen is a concern. A growing one.