"He's playing well and I like the way he's catching," said Padres manager Bud Black. "He's doing a good job with the pitching staff and our team ERA is really good when he's catching."
Rivera's catching ERA (2.75) is a full run better than Grandal's -- but he's also been making headway at the plate while his playing time has increased.
In the last eight games, he has a slash line of .300/.440/.550 with five doubles and five walks. Not bad for someone known for their prowess behind the plate more than in the batter's box.
"All the work that I've put into with [hitting coaches Phil] Plantier and Alonzo [Powell] is paying off," Rivera said. "The main thing we work on is be consistent with my swing. That's been our main goal since last year."
Rivera is hoping his play will result in him making the leap from third-stringer to full-time starter.
"I haven't really been able to play every day in the big leagues. This is great," Rivera said. "I finally get an opportunity to do it, I'm trying to take advantage."
Black is certainly pleased with Rivera's progress, but he's hoping that Grandal can find his swing after he was suspended for the first 50 games of 2013 for testosterone use before tearing his ACL in July.
"Grandal potentially has a lot of upside," Black said. "A switch-hitting catcher in his mid-20s with some tools, you'd like to think that the guy could grab the job and get the majority of playing time.
"But for now, Rene's playing better."
Will Laws is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.