Portillo signed a professional contract with USL Pro club Charleston Battery on March 19, 2014.[1] He made his professional debut three days later in a 1–1 draw with Orlando City.[2] At the end of the 2014 season, Portillo was voted the club's newcomer of the year after establishing himself as a key starter in central midfield.
After a season with USL side Real Monarchs, Portillo joined MLS side Real Salt Lake on February 26, 2019.[3] Following the 2021 season, Portillo's contract option was declined by Salt Lake.[4]
On December 18, 2021, Portillo joined USL Championship side New Mexico United ahead of their 2022 season.[5] On May 31, 2022, Portillo was named USL Championship Player of the Week for Week 12 in recognition of his brace and assist against Phoenix Rising FC and his additional goal against Indy Eleven.[6]
On November 22, 2023, it was announced that Portillo would join FC Tulsa for their 2024 season.[7] Portillo scored one goal and added two assists in his time with the club.