The description is self explanatory. Players online are tougher opponents then playing against the CPU. The best advice and easiest way I can recommend to getting this achievement is by:
Search for players with the same skill level as you.
Look for people who have the default icon and title. They may be less experienced then you. Look at their win/loss record.
Try to play against your opponent with a good connection.
If you have difficulty online, practice in training, against the cpu, or a friend and experiment with different characters. Using the right assists can make a difference in a battle. Check on youtube too.
Once you get 10 wins, your achievement pops.