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• Ferran Torres scores only goal as Barcelona edge past Porto

  Substitute Ferran Torres snatched the only goal of the game as Barcelona extended their 100 per cent start in Champions League Group H with a hard-fought 1-0 win in Porto.

  The hosts had most of the chances but were undone by a blunder from Romario Baro in first-half injury time which allowed Torres to go through and slide the ball past Diogo Costa.

  It was not all plain sailing for the visitors, who had to survive a torrid late spell which culminated in Gavi being sent off in injury time for a second yellow card.

  On a history-making night for Barca, Xavi named Lamine Yamal in his line-up, making him the youngest starter in Champions League history at 16 years and 83 days old, beating the previous record held by Celestine Babayaro.

  The teenager provided plenty of threat in the visitors’ front line, as did former Benfica star Joao Felix, who was given a tasty reception on his return to Portugal.

  Baro should have done better with a Joao Mario cross in the seventh minute but failed to get his shot off in the box, then Pepe’s touch also let him down after being fed by the dangerous Mehdi Taremi.

  Barca keeper Marc-Andre Ter Stegen comfortably gathered a tame effort from Stephen Eustaquio and it was not until the 23rd minute that the visitors fashioned a real chance when the ball fell to Felix on the edge of the box but he fired just over.

  Robert Lewandowski’s night was ended by an apparent ankle injury on the half-hour mark and he was replaced by Torres, but it was still Porto who threatened with Wendell in particular posing problems down the left flank.

  But Baro undid all Porto’s good work on the stroke of half-time, when his blunder allowed Ilkay Gundogan to intercept and he raced clear and fed Torres, who did the rest.

  Barca came close to extending their lead early in the first half when Yamal poked a shot on the turn at Costa, then Felix almost sprang onto a Torres through-ball.

  But the visitors were grateful to Jules Kounde on 54 minutes after the defender got a foot in to deny what looked like a certain equaliser after Pepe had been sent through on Ter Stegen.

  As the game strayed beyond the hour mark, Taremi and Wendell had half-chances for the hosts, who also had a strong penalty claim rejected by VAR after Joao Cancelo appeared to handle in the box.

  Porto continued to press and Taremi had the ball in the net in the 83rd from a sublime overhead kick but was ruled clearly offside.

  In a torrid final few minutes Gavi was dismissed before Francisco Conceicao twice came close to an elusive equaliser.

• 'It's a Ferrari, you just need the right driver' – ex-FIFA referee defends VAR amid Liverpool row

  Former FIFA referee Duarte Gomes has leapt to the defence of VAR amid the furore surrounding Liverpool's Premier League defeat to Tottenham, calling the technology's introduction "the best thing to happen to football". 

  The use of VAR is a hot topic in the English top flight again after Luis Diaz was incorrectly denied a goal in Liverpool's 2-1 loss to in-form Spurs.

  Darren England – the VAR official on duty at the time – misunderstood the on-field call to chalk the goal off for offside, inadvertently clearing an incorrect decision.

  Liverpool have reacted furiously to the incident, which played a part in their first defeat of the season, with boss Jurgen Klopp suggesting the game should be replayed on Wednesday.

  However, Gomes – a retired Portuguese referee who officiated in FIFA and UEFA competitions between 2002 and 2016 – says the ability of those using the technology is the issue, not the technology itself.

  Speaking to Stats Perform at the Thinking Football Summit, Gomes admitted officials were still adapting to the technology but said it had already righted "thousands" of incorrect decisions.

  "I don't have the slightest doubt that it's the best thing that's happened to football and to referees for decades," Gomes said.

  "I know that we have a big, long way to run yet. It's not perfect, far from that. People who work with VAR are also learning and they are focused always on their careers as a referee on the pitch. 

  "The process of decision-making was completely different, and then you put them in a room with many screens and tell them to decide in a different way they have to adjust. 

  "As with everybody, there are some people who have more competence than others. We are now on that trail to try to be there. 

  "Nevertheless, in factual decisions, let's say, for example, offsides or with goal-line technology, I believe that around the world, thousands and thousands of goals have been saved or cancelled correctly after VAR. 

  "So yes, it's good for football. It's a Ferrari, you just have to have the right driver to be there.

  "I've made many mistakes with the human eye; penalties, decisions, yellow or red cards, things that I missed. VAR could help me a lot. I would have been a better referee if I had it."

  Gomes also believes, however, that technology cannot become all-invasive in football, emphasising the need to preserve the emotional nature of the sport.   

  "I'm a little concerned about AI in the future, of course also in refereeing matters. I believe it will have an important role," he added.

  "Sitting here right now, I don't know if I will have a different way of thinking in 10 years. We are always adjusting, but I believe technology should always help until the point that humans decide.

  "Human first, technology after, not the other way around because football is for people. It's played for people, with people, and refereed with people, and that's what gives the emotion.

  "If you become very technological, it's very difficult to have an emotional sport and then it will lose many of its values, so yes, technology is always to help, not as a substitute for the referee."

  Gomes also feels the rise of social media has had a major impact on the levels of abuse received by officials. In a high-profile incident from last season, Roma boss Jose Mourinho was given a four-match ban by UEFA for angrily confronting referee Anthony Taylor after his team lost the Europa League final.

  "I believe it's getting worse because social media gives the right to everybody to criticise, especially the ones who didn't do it with a public voice before," he said.

  "Football is a social phenomenon and it's unique because it can put you in a very emotional state, sometimes an irrational state, which is worse. 

  "You cannot ask people to be reasonable when they have their emotions so strongly attached to their teams and their competitions. 

  "Sometimes you have to let the balloon go down a little bit and then ask them for some tolerance again. Nobody wants to hear the explanation of law one or law two, [but] you have to do it slowly, you have to try and try."

• Smith tells Liverpool to move on as Klopp calls for replay of controversial Tottenham fixture

  While Alan Smith accepts Liverpool have every right to be hurt by the VAR error which cost them in Saturday's loss to Tottenham, he thinks Jurgen Klopp's team have no choice but to move on. 

  PGMOL, the body responsible for match officials in English football, admitted a "significant human error" was committed when the decision to disallow Luis Diaz's first-half strike – which was flagged offside – was not overturned. 

  The audio recording of the decision-making process surrounding the incident was made public on Tuesday, revealing VAR Darren England misunderstood the nature of the on-field decision when clearing the check.

  Diaz's wrongly disallowed effort occurred when the game was goalless, with Liverpool down to 10 men following Curtis Jones' straight red card. 

  Diogo Jota was also sent off in the second half before Joel Matip's stoppage-time own goal handed Spurs a dramatic 2-1 victory, maintaining their flying start to the Premier League season.

  Liverpool subsequently said the "sporting integrity" of the game had been "undermined" in a statement, and boss Klopp made further headlines on Wednesday. 

  Speaking at a press conference ahead of Liverpool's Europa League fixture against Union SG, Klopp called for the Spurs game to be replayed, labelling the situation "unprecedented".

  While Arsenal great Smith has sympathy for Liverpool, he maintains the Reds have no option but to accept they were wronged. 

  Speaking to Stats Perform at the Legends of Football event, in aid of Nordoff Robbins Music Therapy, Smith said: "I was amazed when they played on and the offside was upheld.

  "It was a lack of communication, big time.

  "I can't understand how that happened, but it's not great because it casts a shadow over the game, over VAR especially, and Liverpool are clearly very upset. 

  "You can't blame them, but I think you've just got to suck it up and carry on really. It's done. It's done now."

  The incident has sparked further debate about the impact and implementation of VAR, but former Arsenal vice-chairman David Dein says the technology will become more effective as time goes on, calling for supporters to "stick with it".

  "Well, it comes down to two words, human error, and that's going to happen," Dein said. "People have got to understand.

  "I'm a great supporter of VAR. Before VAR came in, the referees were making one game-changing error every three games. That's been reduced dramatically.

  "You'll see as the years go by. It's still in its infancy. It only came in the World Cup in Russia in 2018. That was when VAR was really introduced. 

  "It's going to get better and more efficient as time goes on. I'm a great supporter. You've got to stick with it."

  Arsenal Women's manager Jonas Eidevall was also speaking at the event, and he outlined his belief that semi-automatic offside technology – which is used in UEFA competitions – should be adopted by PGMOL.

  "With VAR, as long as there is a human element to it, there can always be human errors," Eidevall said.

  "If you do the semi-automatic offside technology, you don't really have a human element to that and you get less errors. So I think that's a good example. Goal-line technology is another one. 

  "The referees are also going to get better, over time, at working with a system like VAR. That's also very obvious and they will also learn things every season. They want to get things right."

  Meanwhile, VAR – and goal-line technology – was a hot topic across the opening weekend of the Women's Super League season, with officials failing to award Guro Reiten a goal despite the ball clearly crossing the line in Chelsea's 2-1 win over Tottenham.

  Asked if he expected VAR to grace the league soon, Eidevall said: "Yes, I do. I think that's where the development is heading. I don't know if that's next season or the season after. 

  "I think when we do, if we implement it, it has to be the full version. 

  "What I don't want to see in the women's game is for them to implement a cheaper version of VAR with less camera angles. That makes it really difficult for the referees to see the situations."