Expressions used in Everyday Spoken English in Social and Professional contexts
The 'punch' in this case is the goal or the point which you aim to reach. You might think of it in terms of the 'punchline' at the end of a joke. When you 'beat someone to the punch', you reach a point or achieve a goal that they were also aiming towards. This might happen in the case of two companies competing to sign the same client, or two staff members competing for a promotion: "Well, John beat me to the punch. The Manager confirmed his promotion this morning." You will hear this used in lots of contexts, social or professional.