Herrera (1-1) gave up solo homers in the eighth inning to Jason Heyward, Justin Upton and Dan Uggla and the
Royals could not recover in a 6-3 loss to the Braves on Tuesday night.
"He was throwing the ball good," Yost said. "Location wasn't very good. A lot of pitches were up and kind of down the middle, but he's been almost unhittable all year long."
The Braves have won 10 straight games -- their best streak since April 15-May 2, 2000 -- while Kansas City has dropped three of four.
Royals starting pitcher Jeremy Guthrie gave his team a chance to win despite allowing a pair of solo homers to Juan Francisco and leaving for a pinch-hitter in the eighth with the score tied 2-2.
But Herrera, who began the game with two saves and 5 1-3 scoreless innings this season, fell apart after facing Heyward with one out.
Heyward hit the go-ahead homer with an opposite-field shot into the left-field seats. Upton and Uggla followed to make it 5-2.
"I've got all the confidence in the world in that guy," Kansas City right fielder Jeff Francoeur said of Herrera. "Send him out there tomorrow. I feel he'll go one-two-three. For him, it was one of those nights."
Eric O'Flaherty (3-0) allowed one hit and struck out two in a scoreless eighth for the win in relief.
Herrera allowed three hits, four runs and one walk in two-thirds of an inning.
After Francisco walked to chase Herrera, Chris Johnson followed with an RBI single off Aaron Crow that scored pinch-runner Jordan Schafer from second.
Luis Avilan recorded the first out of the ninth before seeming to injure his left hamstring. Avilan limped slowly off the field with the help of trainer Jim Lovell and manager Fredi Gonzalez before getting carted off.
Closer Craig Kimbrel finished off the Royals by striking out pinch-hitter Billy Butler, giving up an RBI single to Alex Gordon and retiring Alcides Escobar on a groundout. It was a non-save situation for Kimbrel.
The Royals, who have lost three of four, led 2-1 in the fourth when Salvador Perez reached on Francisco's throwing error, moved to second on Mike Moustakas' single and scored on Francoeur's RBI single.
Except for Francisco, who hit his second homer to make it 1-0 in the second and his third to tie it at 2 in the seventh, the Braves were unable to do much against Guthrie.
Atlanta's first five batters were a combined 0 for 14 with one walk and five strikeouts against Guthrie, who gave up five hits, two runs and one walk with six strikeouts in seven innings. Guthrie was trying to win his eighth straight decision dating to last August.
"I felt good, felt like we mixed it up," Guthrie said. "Francisco had a great game. He took two really good swings and kind of got their team back into the game."
Chris Getz tied it at 1 in the third off Braves starter Kris Medlen. Getz, Kansas City's No. 8 hitter, homered for the first time in nearly four years.
"Tough for us," Getz said. "We were right there. It's one of those things that happens. It's too bad we lost. Too bad (the homer drought) took so long. I saw it on the board as I was hitting, so it definitely added to the satisfaction."
Medlen, who was trying to improve to 17-3 in his career as a starter, allowed six hits and two runs -- one earned -- with no walks and five strikeouts in seven innings.
"If I had to pick somebody before the game who was going to take me deep -- no offense, I wouldn't have picked him -- but he's a big-league hitter," Medlen said of Getz. "He hit a pretty good pitch, I thought. Other than that, I felt like it was a pretty solid outing and when I leave the ball over the plate, I felt it was down, and that's when I got some groundballs with those two-seamers."
NOTES: The Braves held a moment of silence before the game for the victims of the Boston Marathon bombings on Monday. ... Players, managers and coaches for both teams wore No. 42 on their jerseys to honor Jackie Robinson. ... Atlanta committed three errors. ... Getz last homered on July 19, 2009, when he played for the Chicago White Sox. He went deep off Guthrie, who was pitching for Baltimore. ... The Braves have outhomered opponents 25-7 and outscored opponents 68-25 for the best run differential in the majors. ... Francoeur, a former Braves RF, played his first game at Turner Field with Kansas City. He had an outfield assist and went 2 for 4 with an RBI. ... Braves 1B Freddie Freeman said before the game that his right oblique is healing and that he expects to come off the DL as scheduled on April 22 at Colorado. ... Braves SS Paul Janish began a rehab assignment Monday at Triple-A Gwinnett.