Antonio Rudiger appeared to tell Andriy Lunin which way Mateo Kovacic would send his penalty before the goalkeeper made a vital save to help Real Madrid beat Manchester City on Wednesday night.
Footage shows Rudiger frantically pointing to his left - the goalkeeper's right - in the moments before his former Chelsea teammate took his spot kick.
Lunin obliged, diving low to his right to keep out Kovacic's effort. That proved to be the difference as the 14-time European champions reached the semifinals after Wednesday's second leg ended 1-1 over 120 minutes.
After Lunin's heroics, Luka Modric could be seen hitting Rudiger, who celebrated wildly before stepping up to score the decisive spot-kick a few minutes later.
Manchester City had led the shootout after Modric saw his penalty saved by Ederson, only for Bernardo Silva to miss with a dreadful effort that floated straight into Lunin's hands.
Antonio Rudiger appeared to tell Andriy Lunin which way Mateo Kovacic would shoot
The Real Madrid goalkeeper followed Rudiger's instructions and saved from Kovacic
Rudiger celebrated wildly after his former Chelsea teammate was denied from 12 yards
After the game, speculation abounded as to whether Real Madrid's substitute goalkeeper - Kepa Arrizabalaga - had also played his part by warning Lunin that Silva would clip his spot-kick straight down the middle.
Eagle-eyed supporters found footage of Kepa being beaten by a near-identical penalty by Silva during his Chelsea days.
On that day - the 2019 Carabao Cup final - the goalkeeper dived to his right as Silva nonchalantly clipped his effort into the net.
This time, however, Lunin stood still as Silva tried to same trick - a few minutes after the two goalkeepers were seen deep in conversation.
Kepa Arrizabalaga was seen deep in conversation with Lunin shortly before the shootout
Bernardo Silva's lofted effort down the middle was easily saved by the Madrid goalkeeper
Rudiger stepped up to score the decisive penalty as Real Madrid reached the semifinals
Lunin later revealed that the decision to stay put was taken before the shootout.
'I needed to take a risk with one of the kicks, we picked one (to stay in the middle) and thank goodness it worked out in our favour,' Lunin said.
'It's an away Champions League game and we went through a lot of suffering... but I'm very grateful to the team for everything they've fought for. I can't imagine myself running like my team mates did today.'
That save proved the turning point of the shootout as Madrid went on to score their final four spot-kicks and reach the semifinals.
Carlo Ancelotti's team will now face Bayern Munich in the last four after the German giants overcame Arsenal 3-2 on aggregate.