Napoli drew 2-2 with Paris Saint Germain in Group C of the Champions League on Wednesday night.
The Italian side led twice, courtesy of goals by Lorenzo Insigne and Dries Mertens, but were denied what would have been a monumental three points by Angel di Maria's brilliant last-gasp goal.
“We had almost won and are happy with the performance, but are angry and regretful at conceding at the 93rd minute," Ancelotti said, as reported by Football Italia.
Ancelotti continued: "Di Maria can create a shot into the far top corner at the last minute, that’s what happens when you have that much quality in the side."
Speaking about Napoli's chances of qualification from Group C, the Italian manager said: “I think the second leg will be decisive for qualification from this group, we’re playing on home turf and I think that’ll be an extra bonus.”
Ancelotti was questioned about his intriguing defensive tactics, which saw Nikola Maksimovic implemented in a back three when Napoli didn't have possession, and a back four when they did. He said: “With three forwards like that, inevitably PSG don’t have a fantastic balance. It’s also difficult to think they could leave some of them out.
“In the first half, Mario Rui had a lot of freedom because Kylian Mbappé didn’t track back much."
However, PSG made some tactical changes at half-time, shifting to a back-three themselves as Juan Bernat was replaced by Thilo Kehrer. Discussing this, Ancelotti said: "In the second half, PSG changed their system and Maksimovic played at a high level, but they pressed us more in Mario Rui’s area.
“It’s possible they will use that second half system at the San Paolo, but after a while we did adjust and find counter-measures by spreading the full-backs a little wider.
“The help from the two strikers, who took turns to come back and help out, made a big difference. Allan and Marek Hamsik gave us a very important balance in midfield.”
In the Champions League, Napoli next face the reverse fixture against PSG in Naples. The 2-2 draw on Wednesday night has put Ancelotti's side in a good position to achieve qualification from Group C, despite entering the group as underdogs. A victory against PSG would all but guarantee the Italian side's progress to the last 16.