They've been important factors in the American League Wild Card Game win over the Athletics, the three-game AL Division Series sweep over the Angels and the two AL Championship Series wins over the Orioles.
"It's been evident, even in the last two games, how big those guys have been," Royals manager Ned Yost said. "For me, the whole focus has just been get through the first six innings tied or with the lead so we could get to those guys. If we have the lead, I feel like the game's over. If we're tied, I feel like they're going to hold us there until we score a run."
What has developed into a potent routine is Herrera in the seventh inning, Davis in the eighth inning and Holland closing out the ninth.
"All three of them have been dynamite all year long. For a team to have three knockout relievers like we've got, it's pretty special," Yost said. "There are not a lot of teams that have three guys that you can count on to come in and close the door and turn a nine-inning game into a six-inning game."
Davis has pitched in all six postseason games, Herrera and Holland in five each. Yost and pitching coach Dave Eiland sought to prepare them for the postseason with increased work late in the regular season.
"We're going to have take them out of their one-inning comfort zone," Eiland said. "They're going to have to go one-plus, maybe up to two innings apiece, especially Wade and Herrera."
And the workload intensified in the two games at Baltimore. Both Herrera and Davis worked two innings each on Friday night and came back for an inning each on Saturday. Holland logged an inning in each game. Davis got the victory and Holland got the save in both games.
"You've got to anticipate things in the postseason atmosphere that you're not accustomed to in the regular season," Holland said.
ROYALS' BACKEND BULLPEN BOYS IN THE POSTSEASON
Wade Davis (2-0)
Greg Holland (4 saves)
It's not always easy this late in the year.
"If you're pitching back-to-back days at this point in the season, everybody's got something they're dealing with and you just keep grinding it out," Davis said.
"I think we're ready for it," Herrera said. "We know that in the postseason, every day is crucial. The good thing about the playoffs is when you travel, it's a day off."
Sure, the pre-planned time off can help a weary arm. Still, even closer Holland is prepared to go more than one inning if necessary.
Holland was the established part of the threesome, taking over as closer in mid-2012. But Herrera was coming off a 2013 season in which he spent time in the Minors and Davis was a starter for most of that season.
"Kelvin figured out how to become a complete pitcher and how to think about situations, and it's really clicked for him this year," Holland said. "I always knew Wade had good stuff, and you never really know how that's going to transition into going from starter to reliever, so it's been a lot of fun to watch those two guys work."
Eiland finds it fun to watch all three. He worked with a strong bullpen with the World Series-champion Yankees in 2009. But has he seen a threesome as formidable as the Royals' Backend Boys?
"To say I've seen any better in the back three, no," he said.