(CNN) -- Bayern Munich stepped up their Bundesliga title defense with a 1-0 win over Karlsruhe on Saturday as leaders Hertha Berlin lost 2-0 in Stuttgart.
Ribery (left) congratulates the goalscorer Sosa in the narrow win.
Bayern and third-placed VfL Wolfsburg, who won 3-0 at Arminia Bielefeld, closed to within a point of Hertha.
SV Hamburg can also move to within a point of the leaders with a win over Schalke 04 on Sunday, but midwinter leaders Hoffenheim dropped further off the pace with a 2-2 draw at Hanover.
They are five points behind Hertha and badly missing injured striker Vedad Ibisevic.
Bayern, who play Barcelona in the quarterfinals of the Champions League, had playmaker Franck Ribery back in their ranks but strikers Luca Toni and Miroslav Klose were missing.
Ribery made his mark by setting up Jose Ernesto Sosa for Bayern's winning goal in the 34th minute.
Hertha were always struggling at improving Stuttgart, who clinched three points with two goals in four minutes.
Brazilian striker Cacau put them ahead just after the interval with Sami Khedira grabbing the second on 51 minutes.
Another Brazilian frontman Grafite scored in Wolfburg's win over Arminia Bielefeld, his 18th of the season.
Borussia Dortmund captain Alexander Frei converted a 61st minute penalty as they beat UEFA Cup hopefuls Werder Bremen 1-0.