The win, coupled with losses by the Yankees and Orioles, allowed the Angels to gain ground in the American League Wild Card standings, as they're now just 2 1/2 games back.
Royals manager Ned Yost played the percentages by bringing in Collins, forcing Morales to bat right-handed with the Angels trailing, 7-5, with two outs.
"We've gotten behind in some games, and they all haven't worked out like tonight," Angels manager Mike Scioscia said. "I think the important thing is you keep playing baseball. You never know when that opportunity comes or when that break comes. Tonight, we cracked open the door [and got a] big hit from Kendrys. Even though, offensively, those guys kept pressuring us, in the end our bullpen gave us a chance to get back in the game. And we got a big at-bat from Torii Hunter, too."
The eighth-inning drama provided the key moments in a back-and-forth battle between the two clubs. After Morales was announced to bat for Chris Iannetta, Yost opted for Collins, who couldn't get a first-pitch fastball past Morales.
"The situation determined that I had to be aggressive, so I went aggressive -- looking [for a] first pitch to drive. And that's what happened," Morales said through translator Diego Lopez, the Angels' video coordinator.
Collins lamented his offering.
"I just made a working mistake. I just went out there and gave him exactly what he wanted. As a pinch-hitter, you're coming off the bench looking for a fastball and that's it, and I gave it to him. You see the results," said Collins, who took the loss. "That's just a mistake you can't make in that situation."
It was Morales' second career pinch-hit home run, the first coming on Sep. 21, 2009, against the Yankees. It's also the second of the season for the Angels. Alberto Callaspo hit one on May 26 against the Mariners.
Morales now has six pinch-hit RBIs on the season, tied for the most in the AL.
"He's got power from both sides. He's strong. There's no doubt he can drive the ball from the right side," Scioscia said. "This year, it's really clear that any opposing manager wants to get him on the right side. It was the right move to make, and fortunately he came through."
But the two-out rally in the eighth didn't end with Morales' blast. Mike Trout and Erick Aybar hit back-to-back singles, and Collins hit Albert Pujols with a pitch to load the bases. Following another pitching change, to Jeremy Jeffress, Hunter walked to give the Angels a lead for good.
"It shows fight," Hunter said. "Guys working the counts, getting big hits when they needed to, getting on base, taking those walks. Pujols got hit by a pitch that inning. Things worked out in our favor tonight, and we'll take it."
The Angels added an insurance run in the ninth, with Kole Calhoun driving in a run on a fielder's choice.
All this after the Angels went down by a crooked number for the second time in the game.
Starter C.J. Wilson gave up two solo home runs in a five-pitch span in the bottom of the second, and the Royals scored again in the third to take an early 3-0 lead.
But the Angels countered, putting up four runs in the fourth inning against Royals starter Bruce Chen. Aybar bunted for an infield single to lead things off, and two batters later, Hunter walked. Howie Kendrick then smacked the first pitch of the next at-bat into left field for a two-run double, cutting the Royals' lead to 3-2.
Vernon Wells was then hit by a pitch, and runners moved to second and third on a wild pitch. Chen struck out Mark Trumbo for the inning's second out, but the Angels took the lead when Callaspo lifted a two-run single into right field.
But the lead was short-lived, as a Mike Moustakas sacrifice fly and a two-run homer from Jeff Francoeur in the sixth gave the Royals the lead again. The teams traded runs in the seventh before the Angels' three-run outburst in the eighth.
As Scioscia mentioned, the Angels bullpen did step up. Six pitchers combined to allow just three runs (one earned) after Wilson left the game following the fifth.
Jordan Walden earned the win, his third of the season, and Ernesto Frieri pitched a scoreless ninth for his 19th save.
"You're just seeing the fight, guys wanting it," Hunter said. "This ballclub over there, they've been giving us trouble the last couple of years. We went out there, we fought those guys, we battled those guys, and they're really trying to be spoilers right now. Just can't give up. We didn't, and we showed it today."