KANSAS CITY — As the Royals push forward in their rebuild, they know the one area that has to improve is their bullpen.

Kansas City’s ‘pen came into Wednesday night’s series finale against the Braves with the second-worst ERA (5.04) in the American League to Baltimore’s 5.68. And Royals relievers were front and center of a 10-2 loss to the Braves at Kauffman Stadium.

In his final start of 2019, Royals left-hander Mike Montgomery labored, but he limited the damage. He gave up two runs over 4 2/3 innings — both coming with two outs in the fifth.

After getting two quick outs in the fifth, Montgomery walked Ozzie Albies after getting ahead of him 0-2. Josh Donaldson then belted an RBI double to left-center. Nick Markakis followed with an RBI single to center, tying the score.

But right-hander Jacob Barnes, who got the final out of the fifth inning, gave up a single and two walks to load the bases in the sixth. Right-hander Heath Fillmyer came on and gave up a two-run single to Dansby Swanson and a sacrifice fly to Albies, and the rout was on.

Barnes’ ERA ballooned to 7.39.

After Tim Hill pitched a scoreless seventh, right-hander Jesse Hahn gave up two hits, two walks and four runs in the eighth in one-third of an inning. Hahn, who is trying to come back from elbow repair surgery, now has a 13.50 ERA in his six outings.

Kyle Zimmer, also making a comeback several injuries, gave up a run in the ninth — his ERA is 11.42.