"When you play so well, when you produce a game of high quality and have so many chances to win, the frustration comes, " Mourinho said after the match.
"Everybody knows we didn't deserve to lose the points."
The Portuguese coach continued: "You have to look at the producers of the game - one team wants to win, the other team wants to draw.
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"The keeper... had two or three very good saves. The post also did very well for them."
O'Neill himself could only pay tribute to his side, who are unbeaten in eight matches this season.
"Obviously we got off to a very poor start, but after 10 or 12 minutes we started causing them problems," the Northern Irishman said.
FOOTBALL Martin O'Neill Aston Villa
Image credit: Imago
"We were under severe pressure in the second half, especially in the last 20 minutes, but I think we did very well.
"We could have come here and caved in. But we didn't."
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