The verb ‘to seal‘ has many meanings, but in football it is used to mean decide, secure, get. You can say to seal the points, which means win the game and get 3 points. If you said seal a point, this would mean a team has come back to secure a draw and get one point. Of course, you will also hear seal the win. The phrase is often followed with an explanation of how the points or victory were achieved, for example, The striker sealed the win with a last minute header.’ To seal. (see also, Seal a deal)
For example: The visitors sealed the points when Fer carried the ball into the 18-yard box before shooting beyond Myhill. (BBC) For example: Agüero had been on the pitch only eight minutes when he sealed the win in stoppage-time.