MANCHESTER, England — Cristiano Ronaldo was walking off the field, a winner once again at Old Trafford, when two young fans brandishing cell phones attempted to get to the Portugal superstar.

One was rugby-tackled to the ground by security staff; the other was forcibly held back. But the five-time world player of the year hung around and, with a broad smile, eventually gave them the selfie they craved.

Ronaldo certainly enjoyed his return to former club Manchester United on Tuesday.

Juventus, Ronaldo’s new team, beat United 1-0 for a third straight win in the Champions League, moving the Italian club to the brink of qualification just halfway through the group phase.

Unlike the last time he was at the stadium — for Real Madrid in 2013 — Ronaldo didn’t score but he was involved in the only goal, sending in a cross from the right wing that was eventually swept home by Paulo Dybala in the 17th minute.

Dangerous going forward and typically obdurate at the back, Juventus delivered a powerful performance that extended its unbeaten start to the season to 11 games and strengthened its status as one of the serious contenders for the Champions League — a competition it hasn’t won since 1996.

With Ronaldo leading the attack, this might be its best chance in years to end the drought.

“We played against one of the biggest — really biggest — candidates to win the Champions League,” said United manager Jose Mourinho, who was effusive in his praise for the Italian side.

Not just of Ronaldo, but especially of Juventus’ two dominant center backs.

“Mr. Bonucci and Mr. Chiellini could teach classes in Harvard on how to be a central defender,” Mourinho said.

This was another chastening loss — a fourth of the season — for United, highlighting the gulf between the heavyweights of the continent and what was once England’s top team. Juventus toyed with United at times, especially in the first half.

He was always going to be the focal point of this game anyway but attention grew even more in the wake of an allegation of rape against him in the United States. Kathryn Mayorga filed a civil lawsuit last month in Nevada claiming the Portuguese star raped her in his Las Vegas hotel room in 2009. Police also reopened an investigation into the allegation at her request. Ronaldo’s attorney, Peter S. Christiansen, issued a statement on Oct. 10 denying wrongdoing by his client.

Five years ago, Ronaldo was introduced as the “magnificent seven” when he came to Old Trafford — where he played for United from 2003-09 — with Madrid for a last-16 match in 2013. He was given a standing ovation by United fans that night and ended up scoring the winning goal to eliminate his former club from the Champions League.

On Tuesday, Ronaldo wasn’t given the big build-up by the stadium announcer as the team lineup was read out but his name was cheered loudly by home supporters. And a few minutes into the game, a fan came onto the playing surface from the Stretford End stand and got to within a few meters of Ronaldo at the other end of the field before being stopped by slow-reacting security.

As he lay on the ground, the fan stretched his arms toward Ronaldo, almost pleadingly.

Then came the incident involving the pitch invaders at the end of the match. Ronaldo was applauded by fans for giving them their selfie.

During the match, Ronaldo’s flicks, tricks and power were all on display as he switched from the left flank to a central position. However, Dybala was arguably the most impressive of Juventus’ attackers and the Argentina international grabbed the winner.

Ronaldo delivered a cross from the right wing, United defender Chris Smalling got in front of Juan Cuadrado at the near post to block the ball but it fell to Dybala, who converted from the edge of six-yard box.

United took a while to get going, having already arrived at the stadium later than planned because the team bus carrying the players got stuck in traffic around Old Trafford. The same thing happened before United’s last home group game, against Valencia, but this time kickoff didn’t need to be delayed.

Ronaldo had a free kick late in the first half batted away by United goalkeeper David De Gea, who then tipped over a fiercely struck shot from the Portugal forward soon after halftime.

United rallied in the final half hour, and Paul Pogba saw a curling shot hit the post before bouncing off goalkeeper Wojciech Szczesny to safety.

“What the players showed today,” said Juventus coach Massimiliano Allegri, “was when to slow the game down, when to speed the game up.”

Juventus has nine points, five more than second-place United.