The Royals' second consecutive win gave them a 2-1 series triumph over the Cardinals. The clubs will meet again in Kansas City in August.
After being held to four hits in the first nine innings, the Royals pieced together four more in the 10th, starting with inning-opening singles by Jorge Soler and Alex Gordon.
An error by Cardinals reliever Bud Norris (1-1) loaded the bases, setting the stage for Butera's tiebreaking hit.
One out later, Jon Jay singled in a third run, capping the scoring.
Blaine Boyer (2-0), the fourth Royals pitcher, was credited with the win after throwing a scoreless ninth inning. Closer Kelvin Herrera recorded his 10th save with a 1-2-3 bottom of the 10th.
Both teams held early leads, the Royals taking theirs when Salvador Perez connected off Cardinals starter Michael Wacha for his eighth home run of the season leading off the second to open the scoring.
The Cardinals countered immediately with a pair in the bottom of the second after Tyler O'Neill had singled and Jedd Gyorko doubled to open the inning.
Harrison Bader tied the score with an infield out before Francisco Pena plated Gyorko with a two-out double that put St. Louis up 2-1.
The Royals tied the game in the sixth on Whit Merrifield's sacrifice fly.
Both starting pitchers went without a decision despite effective outings.
Royals right-hander Jakob Junis worked the first five innings, allowing two runs and five hits. He walked one and struck out seven.
The Cardinals' Wacha was pulled two outs into the seventh, having given up just one earned run (two total). He allowed four hits and struck out six without walking anyone.
Gordon had two hits for the Royals, who improved to 2-3 both in interleague play and in extra-inning games.
Pena had a single and a double for the Cardinals, who completed a 3-4 homestand.
The Royals out-hit the Cardinals 8-6.
--Field Level Media
Kansas City | St. Louis | |
Jakob Junis | Player | Michael Wacha |
No Decision | W/L | No Decision |
5.0 | IP | 6.2 |
7 | Strikeouts | 6 |
5 | Hits | 4 |
3.60 | ERA | 1.35 |
Kansas City | St. Louis | |
Alex Gordon | Player | Francisco Pena |
2 | Hits | 2 |
0 | RBI | 1 |
0 | HR | 0 |
2 | TB | 3 |
.500 | Avg | .500 |
Team | Hits | HR | TB | Avg | LOB | K | RBI | BB | SB | Errors |
Kansas City | 8 | 1 | 11 | .229 | 7 | 10 | 5 | 2 | 1 | 0 |
St. Louis | 6 | 0 | 8 | .171 | 9 | 12 | 2 | 2 | 0 | 2 |