Peter Walton has clarified the correct decision was made when Kai Havertz was ordered to retake his penalty after both Chelsea and Dortmund players encroached on the box.
The former professional referee was called upon to provide insight on what played out at Stamford Bridge on Tuesday for BT Sport after referee Danny Makkelie spotted an infringement as Havertz hit the post with his spot-kick.
Makkelie ordered that Havertz take the penalty again - which the Chelsea star scored - after players from both teams encroached on the box, with Walton explaining that the match official made the correct call.
Walton said on BT Sport, as he watched a replay of both Dortmund and Chelsea stars entering the area before Havertz had made contact with the ball on the spot: "That is encroachment, yes.
"He's clearly in the area there, and what it is is he has a material effect on the ball. The ball comes back off the post and when you see it, it's the player who's encroached who clears the ball."
According to FIFA laws, the rules are slightly different depending on who encroaches and whether the ball hits the back of the net.
If the attacking team encroaches on the box and the spot-kick is scored then it must be retaken. If it is missed, then an in-direct free-kick is awarded.
If the defending team encroaches on the box and the spot-kick is scored then the goal stands. If the penalty is missed, then it is retaken.
And finally, if players from both teams encroach on the box, as was the case in Tuesday's Champions League last-16 second-leg clash at Stamford Bridge, then the penalty is always retaken - regardless of the outcome.
As it was for Dortmund, Chelsea missed their spot-kick, which means that they drew the long straw on this occasion, despite players on both teams being, technically, in the wrong.
Dortmund went into the clash with Chelsea a goal to the good after beating them 1-0 at Signal Iduna Park in the first leg.
Graham Potter is under growing pressure at Chelsea, but his side won last time out in the Premier League against Leeds.
And they took the lead through Raheem Sterling just before the break after dominating the game in the first half on Tuesday.
The Blues doubled their advantage after the break following Havertz's two attempts from the spot - with the German slotting home with his retaken effort.
