Hitz fumbled Jonathan Schmid’s second-half shot to hand Freiburg their first win against Dortmund since 2010. The loss left Dortmund three points and two places adrift of the top four.
A long-range effort from South Korean youth international Jeong Woo-yeong gave Freiburg the lead just after half-time, before Hitz allowed Schmid’s shot to slip through his fingers at the near post minutes later.
A late strike from 16-year-old Youssoufa Moukoko was not enough to rescue a point for Dortmund.
Elsewhere, former Arsenal defender Shkodran Mustafi endured a difficult debut for Schalke as a 3-0 defeat at home to RB Leipzig kept his new club rooted to the bottom of the table.
Nordi Mukiele gave Leipzig the lead at the end of a turgid first half, beating Mustafi in the air to head the ball in at a corner.
Marcel Sabitzer put the game beyond doubt in the second half, sweeping a low shot past Mustafi and goalkeeper Ralf Faehrmann, before Willi Orban headed in Leipzig’s third.
The win kept second-placed Leipzig seven points behind league leaders Bayern Munich, who had temporarily extended the lead to ten with their 1-0 win at Hertha Berlin on Friday.
Both Wolfsburg and Bayer Leverkusen remained hot on Leipzig’s heels with wins on Saturday.
Second-half goals from Wout Weghorst and Ridle Baku gave Wolfsburg their fifth win in a row away to Augsburg, while Leverkusen were 5-2 home winners in an entertaining clash with Stuttgart.
Kerem Demirbay put Leverkusen in front with a neat backheel volley from close range on 18 minutes and nutmegged Stuttgart goalkeeper Gregor Kobel to double the lead shortly afterwards.
Sasa Kalajdzic struck twice in the second-half, but his second was a mere consolation goal. Leon Bailey and Florian Wirtz had already given Leverkusen a commanding lead.
English winger Demarai Gray, who joined Leverkusen from Leicester City in January, added a fifth before full-time on his debut to pick up his first Bundesliga.
Elsewhere, second-from-bottom Mainz moved to within four points of safety as Moussa Niakhate’s first-half penalty gave them a hard-fought 1-0 win at home to Union Berlin.