English Club Manchester United started their Europa League campaign with a 1-0 defeat at home to Real Sociedad.
Brais Mendez scored the only goal of the match from the penalty spot following a controversial call that saw a handball decision go against defender Lisandro Martinez. While United protested the decision, VAR decided to uphold the on-field referee's call.
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In the earlier game on Thursday night, Premier League leaders Arsenal got their Europa League campaign off to a winning start by beating FC Zurich 2-1.
The Gunners took the lead in the 16th minute through debutant Marquinhos. And while Zurich equalised before half-time through a penalty, Eddie Nketiah's 62nd minute goal sealed the tie in Arsenal's favour.