The 20-year-old, signed in the summer from Valencia, played as a central striker in France, a change from his usual wide position.
But he was superb throughout, scoring City’s opener and providing a constant threat with his pace and quick feet.
Guardiola says he has adapted to life at City quickly and believes he showed selflessness to play in an unfamiliar role in difficult circumstances against Marseille's back five.
“He has settled really well,” he said. “Ferran is not a striker. I would congratulate him for making the effort to play in this position.
"He scored the goal. It is not easy as a striker against five defenders.
"We don’t have many options until Sergio and Gabriel come back, so we had an alternative playing Ferran in this position."
City are now three points clear at the top of Group C having won both our matches so far.
It’s a fine start to the campaign, with two difficult assignments negotiated with relative ease.
It puts us in a strong position to qualify with games to spare, something Guardiola would welcome given our hectic fixture schedule.
He was delighted with the application and professionalism of his players in France – but says it’s no different to what he has seen since arriving in Manchester in the summer of 2016.
“Our application is exceptional from the first day I have been in this club," he said.
"Sometimes the opponents are better than us, that is life.
"I know when you win you are a master and when you lose you are a disaster.
"It is important to start the Champions League with two victories because we are so close to being in the last 16. But still, it is the beginning. We are still improving.
"I saw the mentality from the first five minutes, the way we played. We were incredibly patient to wait for the right moment to score and not concede counter attacks.
"For 15-20 mins they were better. We defended well in the box. In general it was a good performance because in Europe I know how demanding and difficult it is.”
Guardiola also praised City’s defensive solidity.
And Kyle Walker’s exceptional form continued with another brilliant display at right-back.
Guardiola was impressed with what he saw and was delighted with the clean sheet.
“We were so stable,” he said. “Ruben and Laporte were good.
“Walker is in best form since we have been here in Manchester.”
City return to Premier League action on Saturday as we face Sheffield United in the day’s early kick-off.
And although Guardiola admits it will be one of the toughest domestic assignments of the season, he wants his players to enjoy tonight’s win and take some to rest before attention turns to the weekend’s game.
“It’s one of toughest games away in Premier League,” he said.
“Sheffield were so good last season.
“Now we enjoy today, tomorrow we are off and then we prepare for Sheffield best we can.”