You are of course right, I was at a match earlier this season Spurs vs Man Utd at White Hart Lane. Man U were useless in the first half and Spurs were brilliant. At half time it was 3-0 to Spurs, the Spurs fans were loving it (a paper reported the next day that one Spurs fan even bet 10k on Spurs to win, his return was going to be 600 pounds).
Come the second half Man U stunned them with an early goal and Spurs absolutely shit themselves. You probably know but United walked all over them and were extremely classy winning 5-3.
Bye bye 10k, the moral of this story is "Never bet against Man U and never write them off"