Christopher Nkunku and Mykhailo Mudryk scored the goals in the second half, Jadon Sancho’s cut-back shortly after the interval finding the France international who fired in his 11th of the season, then Mudryk finished things late on with a lovely finish into the top corner.
Manager Frank Schmidt has spent 17 years in charge of Heidenheim, leading them from the fifth tier of German football to the Bundesliga and into Europe, and they defied their humble status to give Enzo Maresca’s side, who had Cesare Casadei sent off in stoppage time, their toughest challenge this season in Europe.
The Italian head coach – Chelsea’s 18th during Schmidt’s reign – again called upon his second string, making 10 changes from Saturday’s Premier League win over Leicester.
That meant a start for striker Marc Guiu, and the 18-year-old went close early on when trying to beat Kevin Muller at his near post from Mykhailo Mudryk’s pass, the goalkeeper down quickly with a smart stop.
Teenager Paul Wanner, the Bayern Munich loanee, tested Filip Jorgensen in Chelsea’s goal, then Guiu drew another block from the legs of Muller.
Kiernan Dewsbury-Hall was next to go close for the visitors, hitting a fierce drive from range that the goalkeeper turned behind for a corner. Wanner then had the best chance of the opening 25 minutes, stealing in behind Chelsea’s defence and firing towards Jorgensen’s near post, denied by a fine reaction stop from Maresca’s number two.
Tosin Adarabioyo, who scored his first goal for the club during the 8-0 demolition of Armenian side Noah earlier in November, arrived to meet a whipped free-kick on the stroke of half-time, his poke sailing fractionally past the post as Chelsea came within a whisker of going in ahead at the break.
The breakthrough arrived five minutes after the interval. Axel Disasi put in a bullish challenge to win the ball in midfield, allowing Dewsbury-Hall to take up possession. He worked it wide on the right to Sancho, whose cross was collected via a deft first touch by Nkunku who crashed it into the far corner for 1-0.
Having fought hard for their lead it was nearly whipped away from them within minutes. The defence dithered in trying to clear the ball from the edge of the box and it broke to Leo Scienza who lashed it low and hard, first time towards the bottom corner, but there again was Jorgensen with a save.
Moments later, Scienza went close again with an audacious, curling effort from outside the box which Jorgensen was relieved to see drop inches wide of the post.
Chelsea’s goalkeeper was being given the most thorough examination of his Chelsea career. He pulled off an outstanding block to deny Wanner when the 18-year-old went clean through in the 69th minute.
The offside flag saved Chelsea after Maximilian Breunig’s header found the top corner.
But the visitors would have the last word, Mudryk meeting Sancho’s low cross with a brilliant, rising effort into the roof of the net four minutes from time.