The Blues matched Atletico Madrid’s previous best of 15 games unbeaten, after beating Slavia Prague in the quarter-finals.
Chelsea’s record-breaking run began back in 2012, the season in which they lifted the Europa League trophy.
Luka Jovic’s superb first-half header saw Maurizio Sarri’s side fall behind in Germany, but Pedro levelled for the Premier League team shortly before half-time.
The second leg will be played at Stamford Bridge on Thursday, May 9.
