MINNEAPOLIS, Minn. -- The Red Sox rank third in the American League in reliever ERA (3.03), WHIP (1.19) and batting average against (.218).

But president of baseball operations Dave Dombrowski needs to acquire at least one setup man before the July 31 trade deadline. He should be pursuing a top impact reliever, such as Padres' Brad Hand or Orioles' Zach Britton and Brad Brach.

Delve deeper into the statistics. Red Sox relievers have pitched fine against the Rays, Blue Jays, Orioles (and those types of teams). But weaknesses get exposed when facing the best clubs.

Joe Kelly, Matt Barnes and Heath Hembree, Boston's top three setup men for closer Craig Kimbrel, all have pitched poorly against the Yankees, Astros and Mariners:

~ Kelly has allowed five earned runs, eight hits and six walks in 6 2/3 innings against the Yankees, Astros and Mariners. He has a 6.75 ERA and 2.10 WHIP vs. the three clubs.

~ Barnes has allowed six earned runs, six hits and four walks in 7 innings against the Yankees, Astros and Mariners for a 7.71 ERA and 1.43 WHIP.

~ Hembree has allowed eight earned runs, seven hits and seven walks in 5 2/3 innings against the Yankees, Astros and Mariners for a 12.71 ERA and 2.47 WHIP.

Meanwhile, Tyler Thornburg's return from his injury rehab assignment appears nowhere in sight. He allowed three runs on four hits (one homer) while recording just one out Sunday.

Dombrowski acquired quality relievers at the deadline each of the past two years without trading top prospects.

Brad Ziegler, acquired before the 2016 deadline, and Addison Reed, acquired at the 2017 deadline, didn't cost Dombrowski any top-15 organizational prospects. Ziegler, who posted a 1.52 ERA in 29 2/3 innings, didn't even cost a top 20 prospect.

Relievers come cheap at the deadline, but Hand might be a different story considering he's an elite closer and under control through 2020.

The Red Sox have some talented top-10 organizational pitching prospects. Bryan Mata, only 19 years old, has a 3.29 ERA in 12 starts at High-A Salem.

Mike Shawaryn, a 23-year-old fifth rounder out of Maryland in 2017, has a 3.12 ERA in 12 starts at Double-A Portland.

Jalen Beeks and Chandler Shepherd both have pitched terrific at Triple-A Pawtucket. Shepherd has a 1.93 ERA in his past nine starts (51 1/3 innings).

Other teams also are likely intrigued by Ty Buttrey who is on the 40-man roster, throws 100 mph and has a 0.84 ERA for Pawtucket over his past 21 1/3 innings (16 outings) dating back April 30. He's close to the big leagues.

Josh Ockimey, meanwhile, has intriguing raw power. The 22-year-old first base prospect has a .289/.392/.506/.897 line, nine homers, 12 doubles and 33 RBIs in 51 games for Portland.

Santiago Espinal, a 23-year-old shortstop who Boston drafted in the 10th round in 2016, has made himself a top 15 organizational prospect. He's in the midst of a breakout season, slashing .310/.364/.489/.853 with seven homers, 14 doubles, three triples and 32 RBIs in 58 games for Salem.

The Red Sox have one of baseball's worst farm systems. But that doesn't mean they don't have appealing prospects.

The Royals traded reliever Kelvin Herrera to the Nationals on Monday for the Nos. 10 and 11 organizational prospects.

The Red Sox would need to determine if it's worth weakening the system even more by trading a top 5 or 10 prospect such as Ockimey, Mata, Shawaryn or even 2017 first rounder Tanner Houck for someone like Hand who would be able to take over the closer job from Kimbrel next season.

Kimbrel will be a free agent.

Britton and Brach both will be free agents at the end of the season, too.

Britton likely would be perfect in the postseason as an Andrew Miller-type who could be used in any situation and for multiple innings.

He made seven relief appearances of more than three outs, including four outings of five or more outs, during 2016 when he finished fourth in the AL Cy Young voting.

Britton, who recently returned from a ruptured Achilles' tendon, began his career as a starter like Miller. So he embraced throwing multiple innings as a reliever.

"I was like, 'Yeah, if you want to throw me for three innings, go ahead.' It wasn't something I was scared of or didn't know how to navigate," he told MassLive.com in May.