Christensen was selected by Atlanta United with the No. 70 pick in the 2018 MLS SuperDraft and later signed with ATL UTD 2 on Feb. 18, 2018. He started all 72 games of his four-year college career at Portland and recorded 20 clean sheets. Christensen was twice voted West Coast Conference Goalkeeper of the Year. He played for the Seattle Sounders FC Academy and was the 2011 Generation Adidas U-15 Golden Glove winner.
2018 (ATL UTD 2): Christensen made 10 starts during his rookie season. He made his professional and club debut at Charlotte Independence (3/31). Christensen four saves and posted his first clean sheet of the season at Tampa Bay in a 0-0 draw (6/2). It was the first time Tampa Bay had been shutout at home since August 20, 2016. He made a career-high six saves at New York Red Bulls II (7/6) in a 1-6 loss. Christensen recorded his first professional win, a 2-1 victory, at Toronto FC II (8/31).
2017 (University of Portland): West Coast Conference Goalkeeper of the Year, All-WCC First Team. Christensen is the first WCC student-athlete to claim back-to-back WCC Goalkeeper of the Year honors after finishing his senior season with a league-leading 1.11 goals against average in league-play. The senior also led the WCC with three shutouts while collecting a total of 22 saves. His .733 save percentage ranked second in the WCC. Recorded a total of six clean sheets as a senior. Ends his Portland career fifth in all-time saves, fourth in saves per game and fifth in shutouts.
2016 (University of Portland): West Coast Conference Goalkeeper of the Year, All-WCC Second Team, WCC All-Academic Honorable Mention. Recorded a league-high seven shutouts, second in the WCC in both goals against average (0.91) and saves per game (3.37) and third in overall saves percentage (.780). Produced four shutouts during conference play, including consecutive shutouts at home against LMU (Oct. 28) and San Diego (Oct. 30) en route to nabbing WCC Player of the Week (Oct. 31). Ended season No. 4 all all-time at UP in saves per game (4.27) and is No. 7 in career shutouts (14.0) and overall saves (235).
2015 (University of Portland): Started 17 games, recording three shutouts on the year. Led the league in saves (85) and saves per game (5.00). Shutouts at SMU (Sept. 10), who ended the season No. 9 in the RPI, vs. No. 8 Oregon State (Sept. 17) and at No. 10 Washington (Sept. 27). Recorded a season-high nine saves twice, at SMU and at UW. Ended season No. 2 all-time at UP in career saves per game (4.75) and No. 8 in overall saves (171).
2014 (University of Portland): Started all 19 games and played every minute of the season in goal. Finished with 86 saves and a .748 save percentage. Claimed four blank sheets, including a 1-0 shutout over UCF in his first collegiate game. Also posted a shutout at Florida Gulf Coast (Sept. 4), at home vs. Gonzaga (Oct. 12) and at home vs. LMU (Oct. 31).
INTERNATIONAL: Christensen played for the United States at the U-17 level and participated in its residency program from the fall of 2011 through the spring of 2013.