The Royals had just pulled within 7-6 in the eighth on a two-run double by Brandon Moss -- that barely missed being a grand slam -- and a sacrifice fly by Whit Merrifield. Cain then drove a fly ball deep into the right-field corner near the wall at the 335-foot sign.
For a brief moment, Cain thought he might have given the Royals a lead with a two-run home run. But Cardinals right fielder Jose Martinez grabbed the fly ball just in front of the wall.
During the Royals' last road trip, Cain sneaked a fly ball just inside the Pesky Pole at Fenway Park for a home run.
"I thought it would get in the corner for me," Cain said. "I hit it good, just not far enough. You just never know. I hit a homer in Boston like that. I just know I hit it good. Hope it would get out or at least off the wall. That was a big run at the time."
Alas, the Royals were out of chances after that and fell for the ninth time in 11 games.
Cain, though, now has four three-hit games and one four-hit game in the past 11 days, raising his average to .293.
"At the end of the day, we lost the game," Cain said. "But I'm just trying to get on base as much as possible for the guys behind me."
Cain did have one lapse, though. He was on second base in the third inning with two out and Alcides Escobar up. Cain lost track of the count and got picked off second.
"I thought the count said 0-2 on the board before Esky swung at that last pitch," Cain said. "So when he swung, I thought that was it. I took off my helmet and started walking. Then [Yadier] Molina threw down to second, and it was kind of confusing. But that's my fault. I can't let that happen with a runner in scoring position."
Jeffrey Flanagan has covered the Royals since 1991, and for MLB.com since 2015. Follow him on Twitter @FlannyMLB. This story was not subject to the approval of Major League Baseball or its clubs.