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:
1. Sol Brynn - 6
Conceded four but couldn't really do much about any of the goals. Made a couple of decent saves. 6 Photo: Nick Taylor/Liverpool FC
2. Daniel Dodds - 5
Assisted Boro's goal but struggled to deal with Chong in the second half after the pacey United winger switched flanks. 5 Photo: JPI Media
3. Nathan Dale - 6
Was the closest player to Chong when the United winger added the visitors' fourth. Looks good on the ball though and switched the play well a couple of times. 6 Photo: Frank Reid
4. Marc Bola - 7
Made a few forays forward and coped well with the lively Chong in the first half before the United winger switched flanks. 7 Photo: Frank Reid