The 18-year-old had already had a backheel goal ruled out for offside when he finished Mario Gotze's pass to give Dortmund the lead.

Salomon Kalou poked home Hertha's equaliser but Sancho put Dortmund ahead again from a clever Marco Reus lay-off.

Kalou scored an injury-time penalty to rescue a point for the visitors.

At 18 years and 216 days, Sancho is the second youngest foreigner to score twice in a German top-flight game. Only Son Heung-min, now at Tottenham, was younger (18 years, 135 days) - in Hamburg's 3-2 defeat at Hannover on 20 November 2010.

He has now scored four times in his past three games and had a hand in a goal every 52 minutes this season - five goals and eight assists.

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Dortmund are two points clear at the top of the Bundesliga, with Bayern Munich - champions for the past six years - moving up to second with a 2-1 victory at Mainz.

Leon Goretzka gave Bayern the lead and, after Jean-Paul Boetius' equaliser, Thiago Alcantara scored the visitors' winner from six yards out.