Mikel Arteta made nine changes to his side that beat Brighton in midweek and Arsenal started this game with an unfamiliar three-man defence.
Arsenal, who are usually so dependable at the back, looked shaky at times as a result of that change and the Gunners boss reverted back to a familiar back four after an injury to Leandro Trossard.
Arteta put a lot of trust in both Dowman and Salmon to start a game in a cup competition, and Arsenal became the first Premier League side ever to start with two players aged 16 or under in any competition.
Salmon was tasked with moving into midfield with the ball from defence and to be given such a role in his first start just shows how highly-rated he is by the coaches.
Dowman was arguably Arsenal’s best player in the first half and, despite his age, showed the confidence of a seasoned professional to pick up the ball in dangerous areas while always looking to start attacks.
The youngster has been out since December with an ankle injury but produced moments of brilliance to show why he has been training with the first team squad since he was 14.
Salmon was disappointed to come off after his pass gave Mansfield a route back into the match, but the youngster will have learned a lot from playing in a cup match with such a passionate home support.
Arteta was able to rest key players Declan Rice, Gabriel Magalhaes and Martin Zubimendi, with crucial games in the Premier League, Champions League and Carabao Cup final to come.