The victory lifted Hanover to 57 points, two above fourth-placed Bayern Munich, who could reclaim third with a win at Eintracht Frankfurt on Saturday.
Both teams are battling for a third place finish that leads to the Champions League qualifying rounds. Hanover have now secured at least a Europa League berth, the first time they have grabbed a European spot in 19 years.
"We played a near perfect first half," said Hanover coach Mirko Slomka. "We fought on in the second half although the goal we conceded made us a bit nervous." Hanover, missing suspended midfielder Sergio Pinto and top striker Didier Ya Konan, allowed the hosts more space early in the first half, waiting for their chance to break.
They finally pounced in the 24th minute when Mohammed Abdellaoue was sent through by Jan Schlaudraff with the Norwegian slotting in from the left for his 10th goal of the season.
Schlaudraff then turned scorer, chasing down a smooth Altin Lala pass to round goalkeeper Oliver Baumann seven minutes later before Konstantin Rausch's diving header after a fine run down the right and pinpoint cross by Manuel Schmiedebach sealed their win early in the second half.
Jan Rosenthal cut the deficit in the 79th minute for Freiburg.
Bundesliga leaders Borussia Dortmund, eight points clear, could be crowned champions on Saturday if they beat last-placed Borussia Moenchengladbach and Bayer Leverkusen, in second place, fail to win against Hoffenheim.
