The scoreline didn’t tell the whole story after two late goals from United winger Tahith Chong added to a first-half double from Arnau Puigmal. Boro first-teamers Hayden Coulson, Marc Bola and Marcus Browne all started for Graeme Lee’s side and our Boro writer Joe Nicholson has rated their performances - scroll down and flick through our gallery to see who shone and struggled:
5. Hayden Hackey - 6
Comfortable in possession and kept things ticking nicely in the first half. Saw less of the ball after the break. 6 Photo: FRANK REID
6. Connor Malley - 7
Made several probing runs with the ball and was involved in some good build-up play. Just like the first team, things didn't quite click in the final third for Boro. 7 Photo: JPI Media
7. Ben Liddle - 5
Missed a penalty which could have drawn his side level. Also conceded the free-kick which led to United's opener. 5 Photo: Alex Pantling
8. Hayden Coulson - 6
Was deployed in an advanced right wing position at the start of the match and later switched flanks. Full of energy and drive but his final ball let him down at times. 6 Photo: Jan Kruger