Milan's victory over lazio has not changed anything because in the previous few matches, the AC Milan appeared to be less than optimal. and the results are still just 1 point adrift. as roma and atalanta can threaten their position at any time.
I think the win does help their bid of finishing in the top 4, If they had fail to win the match they'd have drop out of the 4 position by now, after 4 games without a win, I think they really needed that win, Hopefully they can extend the win to their next fixture against Parma.