When he finally got his chance to play in July, he shined by batting .311 with six homers and 16 RBIs in 18 games.
Even when he was asked to fill in at second base for the first time in his career on Wednesday, he happily ran out onto the field and patrolled second for an inning.
And when he was called upon to pinch-hit with the bases loaded and two outs in the bottom of the eighth inning with the Angels down two runs on Thursday, he delivered in a big way.
"We saw the Rally Monkey come out," Rivera said through a translator. "I knew something would happen then."
Rivera, who didn't start for the second game in a row, came into the situation batting .327 with 10 home runs and 92 RBIs in his career with runners in scoring position and two outs.
Those numbers improved when he laced a 1-0 fastball from Rangers reliever Warner Madrigal over the head of center fielder Josh Hamilton to clear the bases and give the Angels their first lead.
"I got a good pitch to hit," Rivera said. "I was just telling myself not to let the pitch beat me. I tried to make good contact, overall."
It was also a big hit for Rivera because entering the game he had been hitting just .224 in August and was battling through one of his worst slumps of the season.
"Juan has been in a little bit of funk lately," Angels manager Mike Scioscia said. "He hasn't been squaring the ball up like he can. But you couldn't ask for a better time to square one up. That was a big hit."
The Angels had scored a run earlier that inning on a bases-loaded walk by Napoli, and they weren't done after Rivera's double, as they added an insurance run on an RBI infield single by Reggie Willits. It added up to five-run inning for the Angels, who entered the eighth down by three runs.
"They're very good," Rangers outfielder Marlon Byrd said. "They don't give up. That's what good teams do. We're a good team and we don't give up. But they know how to play the game, and they shut it down in the end. If you want to be a good team, then they're a good team to watch."
The victory also made Jon Garland an unlikely winner as the right-hander battled back from a four-run first inning.
Garland allowed just three hits, including a solo home run by Chris Davis, after the first to keep the Rangers in check. In all, he tossed eight innings, allowing five runs on eight hits while striking out three and walking one.
"He made good pitches as the game went on," Scioscia said. "He did not have all his tools out there, but he hung in there for eight innings to give us a chance to win."
Garland also got help from third baseman Chone Figgins, who made three spectacular plays at the hot corner after misplaying a ground ball in the first inning.
"The balls got smoked out at him, and he was making great plays," Garland said. "I told him after the eighth inning I was trying to get him on ESPN so everyone could see him. Defensively, he was outstanding."
But the Angels offense was far from outstanding against Rangers starter Brandon McCarthy, who allowed just two runs on six hits over six innings. The Angels hit the ball hard off McCarthy, including a solo homer by Mark Teixeira in the third inning, but they had little to show for it.
"We could have been frustrated early because a lot of line drives weren't falling," Rivera said. "But the guys kept telling each other things would happen and change. I think that was the motivating force."
Garland fell behind early in the first inning, when he allowed a three-run home run to Milton Bradley before allowing a run-scoring double by Davis that went past Figgins' glove.
It looked as though Garland would be knocked out early, but he knew how it important it was for the bullpen to take a breather because Joe Saunders lasted just 1 1/3 innings on Wednesday and reliever Jason Bulger was optioned to Triple-A Salt Lake.
"I told [pitching coach] Mike Butcher at the beginning of the game to leave me out there," Garland said. "It didn't matter if I gave up 10 or threw a shutout. I was going suck it up."
With the win, the Angels have now won two of three after losing eight of 12 before that stretch.
"I'm not going to say I'm happy about this win," Garland said. "But It was a huge comeback win and hopefully we start rolling."