Man City win UCL opener but will need to eliminate mistakes to finally reach the elusive summit

Manchester City will cruise through the group stage of the Champions League -- they usually do under Pep Guardiola -- but against Porto, they were reminded of the type of mistakes they will have to avoid if this is going to be their year.

A 3-1 victory over the Portuguese champions at the Etihad Stadium on Wednesday got their European campaign off to a winning start, though it was not a surprise. City tend to make easy work of the group stage these days, and Porto have not won in England in 21 attempts.

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Still, scratch the surface of the scoreline, and there is work for Guardiola to do if he wants to get his hands on the Champions League trophy for the first time since he won it with Barcelona in 2011. There is plenty of time before the final on May 29 in Istanbul, and group opponents Porto, Olympiacos and Marseille are unlikely to stop the march to the knockout rounds, but once there, City's credentials will be tested.

"We knew how tough it would be," Guardiola said afterward. "The mentality for them is to win every game, and we had to be patient. The result is most important. It was perfect for me -- an incredible performance against a really good team and nice to win. All the teams are good in the Champions League. We made mistakes but generally good."

City have never been beyond the quarterfinals under Guardiola -- Manuel Pellegrini remains the only manager to get to the last four -- and in his prematch news conference, the Spaniard looked back on the defeats to Liverpool, Monaco, Tottenham and Lyon and insisted that not one of those teams was better than his. The difference, in his opinion, was that his players made too many mistakes and, because of that, deserved to be eliminated on each occasion.

There were errors against Porto, too -- lapses in concentration that have proved costly in the latter rounds -- but in the group stages, they are less likely to be punished.

Porto's Luis Diaz took advantage of the first when Ruben Dias' sloppy pass was picked off in midfield, and the Colombian ghosted past Rodri and Joao Cancelo to score. Then it was Ederson giving the ball straight to Matheus Uribe on the edge of the penalty area, though this time the Porto man couldn't finish. Later, only Kyle Walker's lunge prevented Dias from nudging the ball into his own net.

On a different night, City could have gone in at half-time 3-0 down, but this was Porto in the group stages, and instead it was 1-1, with Sergio Aguero scoring his first goal of the season from the penalty spot after Pepe's clumsy jump at Raheem Sterling.

At one point, Guardiola collapsed to his knees with his head in his hands as Porto countered from a stray pass and didn't get up until the danger had been cleared. It was midway through the second half that the home side were finally comfortable, with Ilkay Gundogan producing a wonderful free kick and substitute Ferran Torres, one of the players signed in the summer to make the squad more durable to the challenges of a long season, scoring his first goal for the club.

"Ferran has a sense of goal," Guardiola said. "He's a guy who moves really well, a young player, and the most satisfaction is the way he came in. Always the people who come from the bench are so important."

City are considered among the top contenders to win this season's Champions League, behind favourites Bayern Munich but ahead of a pack that includes Liverpool, Juventus and Barcelona. Although a predictable win over Porto -- featuring handbags, a card-happy referee in Latvian Andris Treimanis and a touchline spat between the two managers -- will do nothing to alter those odds, there were still flickers of the frailties that have led to problems getting over the final few hurdles in this specific competition.

"Porto are incredibly aggressive," Guardiola said. "When you are on the pitch, you see how physical and fast they are. We controlled really well. We were incredibly patient. In these type of games, we learn a little bit."

Guardiola will hope the lessons can help take his team all the way to Champions League glory this season.