Portillo began his collegiate career for the University of Michigan during the 2020–21 season. During his freshman season, he appeared in seven games and posted a 4–1 record with a 1.67 GAA and .935 save percentage.[3] He made his collegiate debut for Michigan on 3 December 2020 in relief of Strauss Mann. He stopped 15 of 17 shots in a loss against Penn State.[4] He made his first career start on 15 January 2021, making 19 saves in a victory against Ohio State.[5]
During the 2021–22 season in his sophomore season, Portillo posted a 31–10–1 record with a 2.14 GAA and a .926 save percentage in his first full season as a starter.[6] He led the nation in saves (1,111) and ranked second in wins (31) and minutes played (2499:13), fourth in win percentage (.750) and ninth in save percentage (.926).[3] He posted his first career shutout on 28 October 2021 in a 3–0 victory against Wisconsin, stopping all 28 shots he faced.[7] During the 2022 Big Ten tournament, he posted a 4–0 record, with a .928 save percentage, as he recorded 90 saves on 95 shots he faced during the tournament. He was subsequently named to the Big Ten All-Tournament Team and named tournament Most Outstanding Player.[8][9] Following the season he was named second-team All-Big Ten, a semifinalist for the Mike Richter Award and a finalist for the Big Ten Goaltender of the Year.[10][11][12]
On 9 April 2022, Portillo announced he would return to Michigan for his junior year during the 2022–23 season.[13] During his junior season, he posted a 25–11–2 record with a 3.00 GAA and a .908 save percentage and helped lead the Wolverines to their second consecutive Big Ten tournament championship and Frozen Four appearance. He finished his collegiate career with a 60–22–3 overall record, 2.49 GAA, and a .918 save percentage.[14]
Professional
Portillo was drafted in the third round, 67th overall, by the Buffalo Sabres in the 2019 NHL Entry Draft.[15] He announced he would not sign with the Sabres and would pursue unrestricted free agency after his college career at Michigan. On 1 March 2023, the Sabres traded his draft rights to the Los Angeles Kings in exchange for a third-round pick in the 2023 NHL Entry Draft.[16][17]
On 10 April 2023, Portillo signed an amateur tryout (ATO) with the Kings' AHL affiliate, the Ontario Reign.[18] On 22 April 2023, the Kings signed Portillo to a two-year, entry-level contract through the 2023–24 season.[19]
On 25 August 2024, Portillo signed a three-year, entry-level contract through the 2026–27 season with the Kings.[20]