The centre-back’s goal handed Hearts a 2-1 win over the Parkhead side to begin their cinch Premiership campaign after a year slumming it in the second tier.
For the club, it was a big occasion. But putting the collective to the side, it was perhaps an even bigger moment for Souttar. One which has been 517 days in the making.
On February 29, 2020, he ruptured his Achilles for the second time in a Scottish Cup clash with Rangers. He ruptured it again that summer.
This time last year the 24-year-old was undergoing rehab.
Even by the time Hearts played their first game of the 2020/21 season, a 1-0 win over Inverness CT in October, there was uncertainty of what lay ahead. Not only with regards to the short-term. But long-term. With his career.
After all, he’d ruptured his Achilles three times, had a hip issue and required ankle surgery. All before he had turned 24.
If anyone on the pitch deserved such a moment it was Souttar, for all that he has come through. But also as a staging post almost, the first day of the rest of his career. Where every occasion on the pitch is enjoyed.
"It was an amazing moment, he said. “Considering last year I was just sitting in the stand for the first game of the season not knowing where my career was going.
"It was a top moment but it is only the start, I’ve got to keep that momentum going.
"We defended well as a team, the goal was disappointing to concede but in terms of the back three and the goalie I thought we defended well and big Craig [Gordon] helped us at the end, which he's going to do because he's an unbelievable goalkeeper.
"We could have been better on the ball at times but that will come and we have to take the positives from today, which is a great start to the season.”
Souttar knows more than most how fragile football is. How quickly things can change. For the meantime he is focusing on the “day to day, enjoying football”.
It will be left to others to speculate about a Scotland return.
More performances like the one delivered at a quarter full but raucous Tynecastle will see Steve Clarke gravitate to EH11.
Souttar has barely put a foot wrong since returning to action at the end of last season. Against Celtic it was a step up in level and intensity. It was a pulsating and, at times, frenetic encounter.
That quality on the ball was on show with Gary Mackay-Steven’s opening goal, striding out of defence to zip a pass forward to Josh Ginnelly in the build-up.
Quicker and stronger
The most eye-catching aspect of the centre-back’s game, however, has been the defensive side. The bread and butter. The heading, the tackling, the battling. In the past, some have sought to question that side of the player’s game.
Currently, such questions can be answered competently and confidently.
At one point, late in the game just before he headed the winner, he produced a great challenge to stop Celtic breaking. Then he lifted his torso up to head the ball while still on the ground to prevent another attack, like a seal doing a trick at a water park.
Souttar is noticeably bigger, but in a good way. Standing the required 1m away, he makes you feel small. He has a more sturdy stature, shoulders Desperate Dan would be envious of. He’s added muscle and he's more robust.
He believes he is in the best shape of his career.
“I worked a lot in the gym with the sports scientist and physios to bulk up a lot and get stronger and quicker,” Souttar explained.
“A lot of work has gone on behind the scenes at Hearts. [Head of performance] Bob McCunn and [sports scientist] Mikey Williams and Craig Maitland in the physio department have worked with me a lot to bulk up and get quicker and get stronger. Thankfully I have managed to do that and taken it into my game as well.
"It’s probably made the defensive side of my game easier. When you are a young boy and you get bullied off the ball and stuff like that. Being stronger and being more robust has definitely helped my game.”
Injury lay-off benefit
Souttar sings the praises of those behind the scenes at Hearts. The team behind the team the supporters don’t see.
Adding muscle mass, getting more robust was one of the benefits of his long injury lay-off. He’d have unlikely been able to do what he has done if he was fully fit but now believes it could be the making of him.
“It would have been difficult because you are churning out games,” he said.
"I’d probably have preferred not to do it but in hindsight when I look back it might be the making of me and the best time it could have happened.
“The whole department is superb at Hearts. The physios and the sport scientists.
"Big Mikey Williams, as soon as I did my injury, was like ‘bang, here’s a programme. This is where you want to be, this is what weight we want to get you to, we want to get you explosive’.
"I’m just doing what I’m told. A lot of the credit has to go to the backroom team at Hearts. They’ve been top with me throughout my time here.”
Taking it game by game, staying fit, there is no limit to what Souttar can achieve.