Rivera, 27, was hitting .349 in 97 games at Las Vegas. A career .323 hitter over six Minor League seasons, Rivera has not hit under .300 at any level since his 2013 stint with Class A Advanced Port St. Lucie.
A promotion to the Majors will be his biggest test yet. The Mets had been hesitant to call up Rivera for several reasons, including his plate discipline -- his Minor League walk rates generally hovered around five percent -- and lack of experience coming off the bench. Though they considered calling up Rivera last week, the Mets opted instead for fellow Minor League veteran Ty Kelly, who has more experience pinch-hitting.
But with Matt Reynolds struggling at the big league level and Jose Reyes recovering slowly from an oblique injury, an opportunity for playing time exists. Capable of manning all four infield positions, Rivera could slot in at third base, with Wilmer Flores shifting to shortstop.
Rivera attended Lehman High School before moving on to college ball at Troy University in Alabama. The Mets signed him as an undrafted free agent in 2011, moving him slowly through their system over the next five seasons.
"That's just always been a part of my game is to put the barrel on the ball," Rivera said earlier this year. "I just try to come to the field every day and put some work in, try to find a way to get better in any way possible -- not just hitting. It's been fun. It's been a blessing. Hopefully I can get that breakthrough this year."
Nimmo, 23, never received much playing time after the Mets recalled him last week as an injury replacement for Yoenis Cespedes. With five other lefty-swinging outfielders on the active roster, the Mets could not find many spare at-bats for Nimmo.
Anthony DiComo has covered the Mets for MLB.com since 2008. Follow him on Twitter @AnthonyDiComo and Facebook, and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.