No. Coach cannot always ensure the victory.

There are so many factors that involves win/loss. Of course when there is no balance between the teams, then high chance of winning by big team will be there. But if big team loses focus and balance between the coach and players goes missing then they are likely to lose the match. No matter how good coach he is, if he manages low team, then he's going to get hard time by bigger teams . Obviously the reason will be bigger budget, bigger name players too. But there is balance in the team, the Coach also plays crucial role. If player plays well but unable to find a goal then they lack some tactical strategy. If Players doesn't well, then there's nothing to do discuss as blame goes to both players and coach.

To ensure the victory balance between should be there between coach and players as in if Coach does his duty to produce great tactics and player implements and plays well, then they are likely to win as we have seen long unbeaten streak games too. There is slim chance to win always at the end. SO NO.