With five teams separated by only four points, the title race is wide open after previous leaders Hoffenheim were thrashed 4-1 at home by Bayer Leverkusen on Friday.
Bayern are in third spot on 38 points with Hoffenheim second on 39, a point behind Hertha. Hamburg, who are level on 36 points with fourth-placed Leverkusen, could move ahead of Bayern with a home win over lowly Arminia Bielefeld on Sunday.
Hertha, missing injured striker Marko Pantelic, took the lead through Ukraine forward Voronin near the end of the first half before Miroslav Klose levelled just past the hour.
Voronin bagged the winner -- his third goal in two matches -- when he took a pass from Raffael and slotted past Bayern goalkeeper Michael Rensing 13 minutes from time.
FAVRE SATISFIED
Bayern's former germany coach Jurgen Klinsmann, returning to the Olympic stadium for the first time since the 2006 World Cup, had warned that his team was ready to top the table.
Instead, it was Hertha coach Lucien Favre enjoying the moment and telling reporters: "I am very satisfied. A win against Bayern -- I think that will do for today. We played as a team and the 2-1 win is deserved."
The home side concentrated on defending early on with Josip Simunic glued to Bayern striker Luca Toni and visiting French playmaker Franck Ribery kept well away from the box.
Hertha slowly grew in confidence and Voronin, on loan from Liverpool, broke the deadlock in the 38th with a well-taken header after Patrick Ebert had found the striker unmarked on the far post with Bayern defender Christian Lell largely to blame.
Bayern looked toothless in attack, especially after Toni went off with an ankle problem, but Klose mamaged to level for the champions in the 61st with his ninth goal of the season.
Hertha keeper Jaroslav Drobny did well to deny Lucio from 20 metres, then blocked two efforts by Bastian Schweinsteiger on the rebound but was helpless when the ball fell to the Germany striker to score with a close-range header.
VORONIN BRACE
Bayern's celebrations were short-lived, though, as Voronin struck again, hitting his second when he took a pass from Raffael, sprinted down the right and slotted past Rensing to the delight of the home fans in the 74,000 crowd.
"We are disappointed and angry," Klinsmann told reporters. "We wanted to get three points here. But now we just have to continue our good run that was interrupted by (defeats against) Hamburg (on Jan. 30) and Berlin."
Stuttgart squandered a two-goal lead but scored a late equaliser through Thomas Hitzlsperger to rescue a 3-3 draw against a gutsy Hanover side.
Stuttgart, in seventh place, have yet to lose under coach Markus Babbel, who took over in November.
Schalke lost 2-1 at Bochum, piling further misery on their troubled season as they stay in eigh
