Meaning of comment "Game. Set. Match."

What's the meaning of p2's comment?

P1: My gf is a doctor and she makes twice as much as I do. F-k I feel like a weird mother f-ker. She makes all the bling at home. I only make around 42k a year as a fund accountant :(. Although she owes a sh-t ton in loans and I'm debt free.

P2: "I'm debt free." Game. Set. Match.

The phrase comes from tennis:

In tournament play, the chair umpire announces the end of the match with the well-known phrase "Game, set, match" followed by the winning person's or team's name.

It is similarly used in other contexts to indicate the winner, often in an argument or a comparison (as is the case here).

It's a reference to a sport (most notably, tennis) that is broken down into matches, which are won by a number of sets, which are composed of games. Saying "game, set, match" is a short way of declaring that you won and/or are the ultimate winner. I.e. "I won the game, which means I won the set, which means I won the match". In this instance, they are using it figuratively to declare that the fact that the first commenter is debt free, is greater than (and trumps) the fact that his girlfriend makes more money than him.