"Tonight's game was pretty clear to me. Against Barcelona you have to defend because they dominate possession but when you have the ball you need to make the most of it," he told a news conference after his team salvaged a last-gasp draw in Paris.
PSG put Barca under pressure in the opening half-hour and David Beckham, the first Briton to represent four clubs in the Champions League, excelled in a holding midfield role.
"His ability to play forward passes was key," Ancelotti said of the 37-year-old former England captain's performance at the Parc des Princes. "He played really well with good passes."
Lucas's dazzling runs wreacked havoc on the usually dominant Barca midfield and Thiago Silva produced yet another awe-inspiring performance in central defence.
"He showed tonight he was the greatest defender in the world," Ancelotti said of the Brazil defender.
But the whole team gradually ran out of steam after Lionel Messi opened the scoring for the visitors from Daniel Alves's superb pass over the defence with the outside of his right foot.
"When you get the ball you need to have good ideas, that's what we had for 30 minutes. We need to do this for the whole 90 minutes," said Ancelotti. "Let's hope we can do that."
Beckham was satisfied with PSG's display, telling reporters: "It's always about two legs these games... I'm happy with the team's performance because we did not lose that game.
"It's important we showed character. It's what got us that result."
PSG twice came from behind thanks to Zlatan Ibrahimovic's close-range strike and a stoppage-time goal from Blaise Matuidi, who is suspended for next Wednesday's return at the Nou Camp.
"It's a blow because Blaise is a very important player. I hope we'll get [the injured] Thiago Motta back. We have other good midfielders, such as Clement Chantome," said Ancelotti.
