MANCHESTER, England — And just like that, everything was exactly as it used to be, as if nothing had ever changed, as if he had never been away. Cristiano Ronaldo had scored, again. Manchester United was winning, again. The fans were exulting, again. He was home, at last, and so were they.

For successive generations of Manchester United fans, Old Trafford was a place of certainty. The vast majority drawn here on Saturday afternoon lived through those days: of crushing dominance and Fergie Time, when a ticket came with a guarantee of satisfaction and seasons ended, reliably, with smiles and glory. Those not quite old enough to remember — a cohort a little larger than the club might like — have been reared on the stories, taught that such was the natural order.

Over the last eight years, though, that surety has ebbed away. Most of the managers tasked with emulating Alex Ferguson have had moments of promise, however fleeting they proved eventually. Louis van Gaal and José Mourinho delivered trophies, though not the ones the club craves. Ole Gunnar Solskjaer, the incumbent, has restored spirit, and belief.

But none has quite been able to make Old Trafford, Manchester United at Old Trafford, feel indomitable again. Even in the midst of their highs, when things seemed to be going well and momentum was building, there was a palpable fragility, as if only the finest membrane separate triumph from disaster. There were too many missteps, too many stumbles, too many days when Burnley or Crystal Palace or Sheffield United turned up here and won. Too often, the guarantee was broken.

The restoration of Ronaldo erases that at a stroke. There has been a distinct giddiness around Manchester United, ever since those whirlwind 24 hours at the end of August — the frantic calls from former teammates, the decisive intervention of Ferguson, his erstwhile manager and ongoing mentor — when he agreed to return.

The delirium, at times, has carried with it just a hint of gratitude, as if an institution as grand as United somehow counts itself lucky that Ronaldo has agreed to grace it with his presence.

The club has devoted its social media feeds almost exclusively to Ronaldo, and has boasted incorrigibly of the sort of numbers he is capable of generating: 700,000 more Twitter mentions than Lionel Messi’s move to Paris St.-Germain, for a start. It hastily redesigned the giant mural that adorns Old Trafford so that he might be at its center. It rearranged its squad — selling Daniel James, asking Edinson Cavani to change his jersey number — so that Ronaldo might wear the No. 7 on his back again.

Perhaps conscious that Ronaldo does not like to have his status questioned — one of his former managers at Real Madrid was once censured by the club for suggesting that Ronaldo was merely among the greatest players of all time — anyone and everyone connected to United has been careful to insist that title is objectively and scientifically his, and not merely a matter of opinion.

Before Saturday’s game against Newcastle, Solskjaer suggested that Ronaldo would be the one who ensured high standards among the rest of the squad, that there could be no slacking with him present, something that sounds an awful lot like it should really be a key part of the manager’s job description. On Friday night, before his debut, it was Ronaldo who addressed the team.

Some of that, of course, can be attributed to the sheer scale of Ronaldo’s stardom, one that he has earned in an era and a culture in which individuals, increasingly, are the brightest lights of all. He has more followers on Instagram than any other person on the planet. He has more followers, in fact, that any single soccer team.

He inspires among a portion of his fan base a loyalty that is sincere and ferocious in equal measure: one that not only brooks no debate about his sporting status, but reacts with fury to any mention of the rape accusation that prompted a feminist group to fly a plane over Old Trafford on Saturday urging fans to “believe Kathryn Mayorga,” the woman who leveled the accusation. Prosecutors in Nevada said in 2019 that Ronaldo would not face charges related to the allegation, though a civil case is ongoing.

To United, though, Ronaldo is more than just an idol. He is a link to a glorious past, too, one in which the world was organized much more to the club’s liking, when it was the unquestioned force in English soccer and, at times, the pre-eminent club in Europe, rather than one of two superpowers in its own city.

And, most of all, he is a reminder of their old certainty. The 36-year-old Ronaldo has built his career on his inevitability. No matter how dire the circumstance or how stacked the odds or how incoherent the logic, Ronaldo would score and his team would win. His raw numbers — the goals scored and the trophies won and the records broken — do more than just illustrate his greatness. They prove his relentlessness.

That is why it is futile to try and impose any sort of sporting rationale on his return. It does not matter, particularly, that he does not really fit into Solskjaer’s tactical scheme or particularly address the flaws that remain in this team.

What matters is that, after United had struggled for 45 minutes to break down an obdurate Newcastle team, Ronaldo appeared to tap in the opening goal. What matters is that, after Newcastle had tied the score, Ronaldo peeled off into enough space to pick up a pass from Luke Shaw, burst into the box, and rattle a shot straight through Freddie Woodman, the Newcastle goalkeeper. What matters is that Ronaldo, on his own, makes Old Trafford certain again.

With only a few minutes left of his debut, with the game settled — Bruno Fernandes and Jesse Lingard had added a little gloss to the score line — and the sun shining, the Stretford End, home to United’s most ardent fans, started to taunt the traveling Newcastle support. “You’ve only come to see Ronaldo,” they sang.

An hour or so after the final whistle, when much of the rest of the stadium had emptied, many of them remained in their places. The postmatch media interviews were taking place on the side of the field, just in front of them. Nemanja Matic and Fernandes and Luke Shaw and Solskjaer had all come out to face the cameras, but they were still not satisfied. “We want Ronaldo,” the fans chanted, again and again, until at last he appeared, with a shy grin and a coy wave. They were still here to see him, too, the man who had made this feel like home.