I think if you look at build-up for Porto, Klopp was adamant that he can't play weakened squad for Porto because it's CL. Which is exactly he did, out of front three he played all except Salah. I believe before Porto, there must have been no mention of man-utd match either. So basically Klopp got less time to prepare his troops for the match whereas Mourinho had a week and it is evident in the efficiency with which UTD players executed the plan. Also, Mourinho had this tactic of targeting our right side planned. Our CBs are good in the air but out of Van Dijk and Lovren, Lovren is vulnerable against more physical opponent, than on Van Dijk's side we have Robertson, who is good defensively and Mane comes all the way down to provide protection. Whereas on right we have inexperienced youngster with little to no protection from Salah. While Man UTD had Alexis, Lukaku and rashford playing against our Lovren and TAA(3 vs 2)