First-half strikes from John Terry and Nicolas Anelka, who converted a penalty, completed a 2-0 victory over the French champions at Stamford Bridge.
The Blues have two wins from two matches and Ancelotti believes they are now well placed to reach the second round.
"I think we're in control of our qualification. This victory was a good step," said the Chelsea manager.
"We have four more matches to play and the next two against Spartak Moscow will be important.
"There is a good possibility that we'll finish in first place."
Other than a purple patch in the second half when Marseille took command, Chelsea were rarely in trouble and hit the woodwork twice in the last 20 minutes through Alex and Michael Essien.
Ancelotti, however, insisted it was anything but an easy night's work.
"It wasn't comfortable because the second half was more difficult as Marseille wanted to get back into the game," he said.
"They put pressure on our midfield and we didn't play as well as the first half but we did create a lot of chances. We had less chance to play from the back.
"The first goal was very good skill from John to score. The game was easier after that but Marseille were in the game until the end.
"They played good football, attacked and wanted to score.
"No, I don't think we were thinking about the Arsenal game on Sunday in the second half."
Anelka's nonchalant 28th-minute penalty may not have been to Ancelotti's liking but the Italian refused to criticise his striker in public.
"I don't tell Anelka how to shoot a penalty. If he scores I'm happy," he said.
"I've never seen Anelka scared or nervous. He's always quiet and calm. He's a good character."
Ancelotti was pleased with the performance of teenager Gael Kakuta, who started in a three-pronged attack alongside Anelka and the magnificent Florent Malouda.
"Kakuta was good, he was involved and played for the team," he said.
"That is the most important thing for a young player. Sometimes a young player wants to show his ability and quality.
"But instead he wanted to play for the team and so I have to congratulate him for his performance."
Marseille coach Didier Deschamps admitted his side had been overwhelmed at Stamford Bridge in their second defeat of Group F.
"We were almost strangled by Chelsea's superiority. We were dominated both technically and physically," said Deschamps.
"We found the first half tough and lacked aggression at times. There was a gap between the teams tonight.
"We tried harder in the second half but they could have added a third. There was a huge difference between the sides."
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