It was born of unfortunate circumstance - but there's nothing accidental about the acute understanding between Jermain Defoe and Scott Arfield.
When Alfredo Morelos threw a stray arm in the direction of Scott Brown to earn himself another red card back in March, Steven Gerrard was presented with a big problem.
Defoe, an 18-month loanee from Bournemouth, had cut an isolated figure whenever tasked with occupying the lone striker role that Morelos had thrived in.
But with the Colombian on the naughty step for four games, the Rangers boss had to find a way to make it work.
Step forward Arfield , literally.
When Defoe nonchalantly let Glenn Kamara's pass roll through his legs, fooling the Celtic defence and allowing his onrushing team-mate to slot home, the striker knew their graft on the training ground had come good.
"For weeks, yeah, for weeks," Defoe told Rangers TV when asked about how long they'd been working on the partnership.
"Not that exactly - when I let it go through my legs - but we've worked on things in training where Scotty runs in behind and I come short, different movements.
"When you're playing with intelligent players, you work off each other. When I watched the goal back, it's unbelievable.
"Glenn (Kamara) just does what he does, and from the corner of my eye I could see Scotty making a run.
"I let the ball come into me and I was going to take a touch, then thought 'if I let this go Scotty might be in'.
"As I turned round, I couldn't believe it to be honest. Even then he still had a lot to do, taking the touch and finishing it.
"But if you look at the goal back, it's amazing."
