To blow a lead
Imagine that your team is playing very well in a match and is winning by two or more goals. Then suddenly the opposing team scores a goal and the dynamic of the game changes. Now your team are edgy or nervous and the opposition are full of confidence and then right at the end they equalise. How did that happen? Your team were much better for most of the game but they ended up blowing the lead – giving the lead a way – they were wining by two goals but finished drawing 2-2 – they blew a two-goal lead. Much like the phrase ‘to blow a chance‘ which means to miss an easy chance, to blow a lead is to lose a lead in a game when your team really should not.
Example: ‘Bayern blow two-goal lead against Wolfsburg.’ (BBC.co.uk, 22nd September 2017).