I had the same circumstances as you. I'm a Lvl 6 and my Opponent was Lvl 8. He beat me 1-3 on my Home Turf, but I didn't give up. I went to war. I played a 4-1-4-1 Formation in the next game and made sure the Win Bonus was maximised and Morale at 100% to ensure my team gave it everything. I began by playing all the Defenders and the DMC with Blue Arrows in the First Half and Red arrows on my Midfield and Striker. Come the Second Half, I put all my team on Red Arrows and gave it everything. I was 3-0 up and at the 90th min, I thought I won, but they scored off a corner and put the game into ET. They ended up winning 4-5 on aggregate. But I won the game 3-2. Anyway, my point is that you can still pull off a victory, even if the team is a higher Lvl. Just need to have hope and a whole lot of Boosters. :P