United have to beat the Portuguese champions by two goals (at least), and Benfica's only away defeat was 2-1 in Moscow.
They even held Barcelona 0-0 in the Nou Camp in the Champions League.
Cup Results
UEFA Champions League 2012-2013
19.09.2012 Celtic away D0-0
02.10.2012 Barcelona home L0-2
23.10.2012 Spartak Moscow away L1-2
07.11.2012 Spartak Moscow home W2-0
20.11.2012 Celtic home W2-1
05.12.2012 Barcelona away D0-0
1 Barcelona 13
2 Celtic 10
3 Benfica 8
4 Spartak Moscow 3
UEFA Europa League 2012-2013
14.02.2013 r2-1 Bayer Leverkusen away W1-0
21.02.2013 r2-2 Bayer Leverkusen home W2-1 (3-1)
07.03.2013 r3-1 Bordeaux home W1-0
14.03.2013 r3-2 Bordeaux away W3-2 (4-2)
04.04.2013 qf-1 Newcastle United home W3-1
11.04.2013 qf-2 Newcastle United away (3-1)
Portuguese Liga 2012-2013
No Date Opponent Venue Result Pos Pts
1 18.08.2012 Sporting Braga home D2-2 3 1
2 26.08.2012 Vitoria Setubal away W5-0 2 4
3 02.09.2012 Nacional Madeira home W3-0 2 7
4 23.09.2012 Academica Coimbra away D2-2 2 8
5 28.09.2012 Pacos Ferreira away W2-1 1 11
6 06.10.2012 Beira Mar home W2-1 1 14
7 27.10.2012 Gil Vicente away W3-0 1 17
8 03.11.2012 Vitoria Guimaraes home W3-0 2 20
9 11.11.2012 Rio Ave away W1-0 2 23
10 24.11.2012 Olhanense home W2-0 1 26
11 10.12.2012 Sporting Lisbon away W3-1 2 29
12 15.12.2012 Maritimo home W4-1 1 32
13 06.01.2013 Estoril away W3-1 1 35
14 13.01.2013 FC Porto home D2-2 1 36
15 21.01.2013 Moreirense away W2-0 1 39
16 26.01.2013 Sporting Braga away W2-1 1 42
17 03.02.2013 Vitoria Setubal home W3-0 2 45
18 10.02.2013 Nacional Madeira away D2-2 2 46
19 17.02.2013 Academica Coimbra home W1-0 2 49
20 24.02.2013 Pacos Ferreira home W3-0 2 52
21 03.03.2013 Beira Mar away W1-0 1 55
22 10.03.2013 Gil Vicente home W5-0 1 58
23 17.03.2013 Vitoria Guimaraes away W4-0 1 61
24 30.03.2013 Rio Ave home W6-1 1 64
25 07.04.2013 Olhanense away W2-0 1 67
26 21.04.2013 Sporting Lisbon home
27 28.04.2013 Maritimo away
28 05.05.2013 Estoril home
29 12.05.2013 FC Porto away
30 19.05.2013 Moreirense home