Rivas signed with Oakland and made his professional debut in 2018 with the Vermont Lake Monsters of the Low-ANew York–Penn League, with whom he hit .285 with one home run, 28 RBIs, and 16 doubles over 61 games, winning the team's MVP award.[8] To begin the 2019 season, he was assigned to the Stockton Ports of the High-ACalifornia League (with whom he was named an All-Star) before being promoted to the Las Vegas Aviators of the Triple-APacific Coast League in late August.[9][10] Over 122 games between the two clubs, he slashed .292/.387/.423 with nine home runs, sixty RBIs, and 26 doubles.[11]
Chicago Cubs
On January 13, 2020, Rivas was traded to the Chicago Cubs in exchange for Tony Kemp.[12] He did not play a minor league game in 2020 due to the cancellation of the season caused by the COVID-19 pandemic.[13] He was assigned to the Iowa Cubs of the Triple-A East to begin the 2021 season.[14] He missed nearly all of May and a majority of June due to injury.[15]
On August 28, 2021, the Cubs selected Rivas' contract and promoted him to the major leagues.[16] At the time of his promotion, he was slashing .284/.405/.411 with four home runs, 32 RBIs, and 13 doubles over 58 games with Iowa.[17] He made his MLB debut the next day starting at first base against the Chicago White Sox at Wrigley Field, collecting two hits in three at-bats as the Cubs lost 13-1.[18] On September 14, he hit his first MLB home run against Kyle Gibson of the Philadelphia Phillies.[19] On September 21, he was placed on the injured list with a finger injury, thus ending his first MLB season prematurely; over 44 at-bats with the Cubs, Rivas batted .318 with one home run and three RBIs.[20]
In 2022 with the Cubs he batted .235/.322/.307. He was designated for assignment on December 23, 2022. He was released on January 5, 2023.[21]
San Diego Padres
On January 12, 2023, Rivas signed a minor league contract with the San Diego Padres organization.[22] In 44 games for the Triple-A El Paso Chihuahuas, he hit .319/.440/.571 with 8 home runs, 33 RBI, and 4 stolen bases. On June 2, Rivas had his contract selected to the major league roster.[23]
On November 2, 2023, Rivas was claimed off waivers by the Cleveland Guardians.[26] The Guardians designated him for assignment on December 15[27] and he was claimed off waivers by the Los Angeles Angels on December 22,[28] who designated him for assignment on January 23, to make room for Robert Stephenson on the 40-man roster.[29] On January 29, Rivas was claimed off waivers again, this time by the St. Louis Cardinals.[30] He was optioned to the Triple–A Memphis Redbirds to begin the 2024 season.[31] He was designated for assignment following the promotion of Ryan Loutos on May 20.[32] Rivas cleared waivers and was sent outright to Memphis on May 23.[33] He was released by the Cardinals organization on September 26.[34]
Personal life
Rivas was little league teammates with fellow professional baseball player Javier Assad when the two grew up in Tijuana, Mexico. Rivas and Assad became teammates on the Chicago Cubs following Assad's promotion in 2022.[35]