United's well-organised and disciplined approach frustrated the hosts, with goalkeeper David De Gea producing two superb saves late on as Liverpool pressed for a winner.
"That was the game we planned," said Mourinho. "We don't want to control the game by having the ball all the time. We adapted to the situation."
"I'm not happy with the game," he said. "We started OK but we weren't brave in possession and didn't wait for the right pass.
"[David] De Gea made two or three great saves but our performance wasn't great. It's a first clean sheet so yippee! But that's all I'm happy about."