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The Red Sox’ rotation represents their most glaring shortcoming to date — but there are hints that it may not be their only weakness.

It seems curious to suggest that the bullpen represents anything but a formidable asset. The relief corps is clearly deeper and better than it was a year ago, not just because of the additions of Craig Kimbrel and Carson Smith but also because of steps forward by Matt Barnes, Heath Hembree, and Robbie Ross Jr.

That said, the anticipated trio of dominant righthanded setup men in front of Kimbrel — Koji Uehara, Junichi Tazawa, and Carson Smith — has inspired questions, if not outright concern.

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Tazawa has been dominant, arguably more unhittable than at any other time in his career as a reliever, a fact that’s played into both a career-high strikeout rate (31.7 percent of all batters faced) and career-high walk rate (a still-acceptable 8.7 percent rate) along with a career-low frequency with which opponents have clubbed extra-base hits against him (3.7 percent).

Uehara, however, has been another story. Even before Tuesday, when he committed a throwing error on a bunt single and then left a fastball over the plate that got tattooed for a homer by Kansas City’s Paulo Orlando, the start of 2016 had been somewhat unusual for the 41-year-old reliever.

From a bottom-line standpoint, Uehara largely has been effective, holding opponents scoreless in 14 of his first 16 appearances before his two-run stumble Tuesday, but some of the signature dominance has been less evident. The long ball by Orlando was the first he allowed this year, part of what Ian Browne of MLB.com accurately portrayed as an uncharacteristic night for the righthander.

Yet almost everything Uehara has done this year has fallen short of the extraordinary standards to which he’s performed throughout his career. His 3.94 ERA is the highest of his bullpen career. He has allowed seven earned runs in 16 innings, two fewer than he permitted in more than four times that workload in 2013.

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His average of 9.6 strikeouts per nine innings is impressive, but still represents the third straight year of decline in that category. He has issued six walks, with his 3.4 free passes per nine likewise representing a career-worst mark.

His velocity has taken another hit, declining for the third straight season to an average of 87.4 miles per hour. And perhaps most notably, opponents are swinging less than ever at his offerings (51.8 percent of pitches) and swinging-and-missing less than ever at pitches in the strike zone (20.5 percent of the time, down from 31.1 percent in 2013).

In other words, Uehara is creating less deception and getting fewer chases than ever, but his strikes are more hittable than ever. That’s a potentially volatile combination, even if Uehara’s mound IQ has permitted him to work through those signs of diminished stuff much of the time.

Smith’s limited usage, meanwhile, has been mysterious, with the reliever having pitched in just three games in his first 15 days since coming off the disabled list. On Tuesday, Smith acknowledged to John Tomase of WEEI.com that his limited workload is a product of days when there’s “a hint of something” in his elbow, a remnant of the spring training flexor strain that affects his recovery time.

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So the blueprint for the bullpen hasn’t quite taken shape as anticipated. Some of its limitations have been offset by the unexpected emergence of other pitchers, and of course the fact that the Sox are crossing the end zone in most of their games has given the team time to sort through its late-innings progression.

Nonetheless, while the rotation will sit in the crosshairs of scrutiny, the bullpen remains a work in progress that may require some reorganization, whether with internal options or eventually from outside the organization.

Koji Uehara stats glance
Chase %: Percentage of pitches outside the strike zone at which hitters swing; Z-Contact %: Percentage of swings at pitches in the strike zone that result in contact (as opposed to swings and misses).
Year 2013 2014 2015 2016
ERA 1.09 2.52 2.23 3.94
Strikeouts/9 12.2 11.2 10.5 9.7
Walks/9 1.1 1.1 2.0 3.4
Fastball velo (avg) 90.1 89.2 88.1 87.4
Chase %* 41.8 39.8 40.3 33.8
Z-Contact %** 68.9 74.3 72.9 79.5
SOURCE: FanGraphs, BrooksBaseball.net

Alex Speier can be reached at alex.speier@globe.com. Follow him on twitter at @alexspeier.