Sevilla break Man Utd hearts in Europa League semi-final - reaction

Comments from the Game:

Sevilla represent everything that is odious with modern football, diving around at every opportunity, lacking class and somehow (somehow) winning a game in which they were outclassed. Utd need a striker, if they had took half their chances they would have scored 6. They must be gutted, Sevilla should be embarrassed.

What is it with managers lately bringing on strikers or fowards with 3 or 6 minutes to go and expecting them to bag goals with such short time?