MANCHESTER, England -- Pep Guardiola said it would be "easier" for Manchester City to defend their Champions League crown than win it for the first time as his team prepared to launch the defence of their title against Red Star Belgrade, but even after starting off with a 3-1 victory at the Etihad, it was clear that the path to a second successive title will have its pitfalls.

If anyone at City -- Guardiola included -- truly believed that winning the Champions League the second time around will be easier just because their blue ribbons are on the trophy, the shock of falling behind to Osman Bukari's 45th-minute goal was a jolt of reality.

"Going down 0-1 at half-time was nice," Guardiola said. "Because maybe we needed it after winning the Treble. We need to be champions who prove ourselves and we proved it."

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The statistics might suggest otherwise, with City mounting 103 attacks compared to Red Star's 13 and creating 37 goal-scoring chances as opposed to three by the Serbian champions, but the numbers only tell part of the story.

Yes, this was a night when City's incredible depth and quality came to the fore as Guardiola's side emerged as victors after two Julián Álvarez goals and a late Rodri strike cancelled out Bukari's surprise first-half opener for Red Star to make it 25 wins and two draws since the Etihad last witnessed a Champions League home defeat in September 2018.

But it was certainly not easy for City and their failure to convert so many of the chances they created might return to haunt them against stronger opponents.

Red Star may have won as many European Cups as City, having lifted the trophy for the one and only time back in 1991, but Barak Bachar's team are not likely to relive the club's finest hour this season or anytime soon.

Yet despite their status as Champions League minnows, Red Star's spirited and fearless approach to their opening fixture in Group G should serve a signpost as to what lies ahead for City this season.

"We tried to be brave, tried to fight," coach Bachar said. "But the way they move the ball is amazing. We can look ourselves in the mirror, though, and say that we had the bravery to face this great team."

The Champions League poses different challenges than City face in the Premier League. In Europe, opponents will play with greater ambition and while that can be a high-risk strategy against a side as ruthless as City, it can also cause problems for even the best teams if they are not fully focused on the task in front of them.

Red Star were given confidence and belief by the array of first-half saves made by goalkeeper Omri Glazer -- the Israel international made six crucial stops before half-time -- and it laid the platform for Bukari to put them ahead with a goal that given by VAR after initially being flagged offside by the assistant referee.

Having been in a similar position against West Ham United at the weekend before going on to win 3-1, Guardiola said that his half-time team talk was a repeat of address at the London Stadium.

"We were playing really well in the last two games, but we missed clear chances and were struggling a bit," he said. "So we said be strong in your head and keep going, and we did it."

Alvarez's equaliser less than two minutes into the second half banished City's nervous tension and put them back on course for victory, but it needed a mistake by Glazer, when he missed Alvarez's free kick with a mis-directed punch, to give City the lead on 60 minutes.

From that point on, a City win was always the likely outcome but, despite their dominance, there is something missing from the side which won the Treble last season.

Some issues are obvious. Ilkay Gündogan has left the club for Barcelona, while Kevin De Bruyne, Mateo Kovacic, John Stones and Jack Grealish are all sidelined due to injury. And it is still early in the season, a time when nobody expects any top team to be at the absolute peak.

But even though City have started the campaign by winning every game they have played so far, they have yet to come up against a likely rival, so their true status is difficult to gauge.

Guardiola is right, though. Winning the Champions League again will be easier for City in the sense that the weight of expectancy and even desperation has been lifted by last June's success in beating Internazionale in Istanbul.

But on the pitch, the task will be as tough as ever and they can thank Red Star for delivering that important reminder.