There are 4 achievements linked to Season mode and luckily you can do them all with the following settings:
• Team Size - 1v1
• Difficulty - Rookie
• Season Length - 9 Weeks
• Playoffs Teams - 4 Teams
You will play a total of 11 matches, 2 play offs and 9 matches and during this time you will face all 9 teams, after winning the first match you will earn this achievement.
Rookie difficulty should be easy enough to win every match anyway as with only one AI they are very stupid. The Ai being stupid means that most of the time you can hit the ball in from the kick off, the 3 times you're positioned almost straight onto the ball boost all the way until you're close to the ball and stop boosting, then keep driving to hit the ball over them and hopefully into the goal (boost too far and it'll hit the top) when you're on the side of the ball boost half way then stop boosting and try to hit the corner of your car on the side of the ball facing away from the goal, takes a bit of practice.
Here's a video of what I mean, using the car 'Ripper'
You will unlock to following on the way: