Three first half Celtic goals, including a twenty-third minute opener from the penalty spot, put the game beyond United's reach by half-time.
United showed much of the spirit which has been evident in recent matches but their promising play faltered after Hasney Aljofree was adjudged to have brought down Larsson.
After the match United boss Alex Smith referred to the importance of the spot kick decision. "We had one or two clear chances and I thought we were a match for Celtic. In my opinion the penalty decision turned the game."
Celtic got a fourth goal midway through the second half to ensure the three points were heading west but Alex Smith remains focussed. "We will keep fighting and battling until we get the breaks."
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