At the main menu you can choose to load into a customs match. I recommend doing 1v1 and setting the bot difficulty to Very Easy and kill to win to 1. Finish the first round by walking off the map and dying. This will follow up by allowing you to ask the bot for a rematch which the bot will always say yes. Now win this round and then you can rematch one more time. After that the matches will be over as the most you can do is best 2 of 3. Rinse repeat this until you have your 100th rematch.