Difference between 肯定 and 确定
肯定 certain; sure; affirm;  (the outcome is virtually a fact)
确定 determine; confirm; finalize (the outcome is already a fact)


You can say, "Team China certainly (肯定) will lose to team Germany in the World Cup." The outcome has not been known yet.  

You can say, "Team China beat team Japan and is confirmed (确定) to advance to the second round." The outcome is known.

But you cannot say, "Team China confirmed (确定) will lose to team Germany in the World Cup." They haven't played yet.


确定 (to finalize): finalize the team roster
肯定 (to affirm): affirm his earlier statement