A man who rarely displays emotion on the field, Rivera lifted his arms in triumph as he was leaving the batter's box, having delivered his most satisfying performance in a season of frustration.
"It has to feel good when you [used to] play for the Angels," Dodgers manager Don Mattingly said. "A three-run homer to put your team ahead, I'm sure you're feeling good.
"Juan's been an RBI guy for us. He's always a pretty good hitter with men on base."
Rivera's homer was just his third after missing 24 games with a left hamstring strain. He hit .274 for the Dodgers last season, driving in 46 runs in 62 games after arriving from Toronto, where the Angels had shipped him with Mike Napoli following the 2010 season in exchange for Vernon Wells.
"I was so happy," Rivera said, denying the assumption that he was more exhilarated than usual in that it came at the Angels' expense. "I stood there for one second and ran hard. It was a cutter or sinker, I don't know. I was just trying to hit the ball hard, do my job."
Rivera was in position to send Dodgers fans home happy in part because Ethier -- capping a long and momentous day featuring his signing of a five-year contract extension -- yanked an RBI single to right after taking what would have been a third strike on a Williams fastball that barely missed in the view of home-plate umpire Andy Fletcher.
"It was a fastball in -- an inch or two in," Ethier said. Asked if it was a tough pitch to take, he replied, "It was a tough pitch to hit, too. Sometimes you've got to take your chances."
Earlier in the inning, Dee Gordon had been ruled safe at second on his third steal of the game and 20th of the season. It was a bang-bang play with second baseman Maicer Izturis handling catcher Hank Conger's perfect strike and catching the body of Gordon as he came in headfirst.
"I hit [Izturis] so hard, I honestly didn't feel a thing," Gordon said, adding that umpire "Joe West said safe."
Rivera had gotten the Dodgers even in the fourth inning with a single to left following singles by A.J. Ellis and Ethier. That was all the resourceful Williams would allow until it unraveled for the veteran right-hander in the eighth.
"He was throwing the ball good," Mattingly said of Williams, who had thrown only 79 pitches through seven economical innings. "He deserved to be in there. I kind of felt bad for him coming off the field, because he really pitched well."
Williams slipped to 6-4 with the loss. Rebounding from his loss in the series opener, closer Kenley Jansen dispatched the Angels in the ninth for his 10th save. The win went to Jamey Wright in relief of hard-luck Aaron Harang.
Rivera, 33, was a quiet 3-for-14 in four games since coming off the disabled list. He spent most of his DL time, when he wasn't playing salsa on his bongos, studying his swing on video, trying to unlock a few keys.
"For a month I was trying to get my swing right," he said. "I was working on mechanics -- my foot, hands, arms, everything.
"I have trouble when I try to do too much. That's when I have a bad swing, when I rush my hands. I have to be short and quick -- quiet with my swing."
Having fellow Venezuelan and former Angels teammate Bobby Abreu at the next locker, offering guidance, also helps.
"We talk about hitting all the time, every day," Rivera said. "Bobby knows hitting. And he knows me."
As recently as 2009, with Abreu's influence, Rivera produced 25 homers and 88 RBIs for the Angels, batting .287. Mattingly had the big man cleaning up, splitting lefties Ethier and Abreu, and Rivera certainly cleaned up against his old friends from Orange County.