related to Sevilla being able to beat Man United was not luck, but Man United's carelessness often happened so that Sevilla could qualify for this semifinal. I would rather admit that Sevilla had a stronger performance than MU in the match at that time and even if we saw the live broadcast of the match we could definitely conclude that Sevilla dominated more in terms of ball possession.
and about Juventus with Sevilla, I find it hard to believe that Juventus can beat Sevilla while Sevilla itself in the European league is in a very strong state and on the other hand from Sevilla's strategy experience can put pressure on Juventus in the second leg later.
Carelessness describes it much better and that is not part of a team's luck. If Manchester United plays careless, which they did, there is always the risk that the opponent benefits from those circumstances. I agree that the two goals happened with some luck in Manchester, but do not forget that both games must be taken together. The convincing argument here for Sevilla is that even if the didn't score the two own goals in Manchester, they would have still won because they won their game in Sevilla by a three goal difference! You can't say that is luck anymore if you are even willing to take away those two goals from them in Manchester. This was a well deserved win.