Englishman Bellingham, who is 17 years and 289 days old, curled a superb 15th-minute strike into the top corner in Dortmund to level the tie 2-2 on aggregate and put the Germans ahead on away goals.
Only one younger player has netted in a Champions League knockout tie -- Bojan Krkic, who scored for Barcelona against Schalke in April 2008 aged 17 years and 217 days.
Bellingham had scored his first Bundesliga goal for Dortmund in their 3-2 win at Stuttgart on Saturday.