2010 FIFA World Cup
44 Achievements
1000
Undefeated Group Stage
Win all three group games and advance to the knockout stage in the Online FIFA World Cup™.
15
How to unlock the Undefeated Group Stage achievement in 2010 FIFA World Cup - Definitive Guide
OlympiakosNYC
You have to win all 3 group stage games online. Pick a strong team like Spain, Brazil, Argentina, England and win all 3 games. It could be hard for the casual player but if you practice enough you should get it. If you don't win your first game you can always Reset the Tournament in Settings till you get your 3 game winning streak.
daenius
From the Main Menu, select "Online FIFA World Cup" and win all three games in the group stage to advance to the knockout stage.
For this, I would recommend using only 5 star rated teams, maybe even go as far as using only Spain (Region is Europe), since they're the best rated team by a long shot.
Select your team, start the World Cup and win all three games in your group to get this achievement.
Again, quitting out of games until you find a weaker opponent might help, although if you're playing with Spain, chances are people will quit out on you often enough, so you should take any chance you get; they're good enough to beat any team.