Kinect Sports Rivals

The TA ratio makes this achievement seem harder than it really is. The easiest way I found to do this was to start up an easy race (only green bar filled), compared to a match with a red or yellow bar. When the countdown for the race started, I made sure my hands were not on the "handlebars". When the countdown hit 1, I grabbed the "handlebars" and this boosted me ahead of the AI. Occasionally, the AI would also boost and get ahead of me which caused me to restart. After a few times of restarting, I was the first person through the first gate and stayed that way for the rest of the race. When you complete a lap a bonus will come up on the left side of the screen underneath your bonus meter. It says something along the lines of "Unchallenged Lap" which means you were first through each gate. Complete one race doing this and then restart the same race to do it again. It only took me a few attempts to unlock the achievement. Good luck.

TL;DR

1. Find an easy race
2. Grab the handle bars when the timer says 1
3. Make sure your boost puts you through the first gate in first place
4. If not restart/Continue being in first place for the entire race
5. Repeat once more for your achievement

If you send or receive a challenge from someone on your friend's list it will be a one on one match making this much easier to obtain. You'll need at least 2 people on your friend's list with the game or take turns trading off with one person. It still took me a few tries to beat my friend's AI bot when sending the challenge so if you're still having a lot of trouble you could try taking turns sending each other challenges where the first person does nothing and see if that helps. Please comment if you try that method and let others know how it goes.