Daley Blind and Ander Herrera had put Louis van Gaal's side in control of Saturday's game before Benteke unleashed a stunning overhead kick to halve the deficit in the closing stages.
However, Anthony Martial's debut goal sealed a 3-1 win for United and condemned Liverpool to a second successive defeat in the Premier League - a result the Belgium international accepts was fully deserved.
"The goal was just instinct," Benteke told Liverpool's official website. "I saw the ball come into the box and I just thought I had to try it.
"I had some luck and I am happy with it, but we didn't get the three points. For my own confidence it was good but, at the end of the day, I would have rather taken the three points and so I'm disappointed.
"In the first half, we didn't play. The second half was a little bit better but, in general, we didn't deserve a victory.
"When I scored, I thought in my mind that maybe we could come back, but they scored to make it 3-1 and that killed our hopes.
"We have to show more. When you play for a club like Liverpool, you have to show more. That's what we're going to do now in training - work hard. Work hard, and try to play well."
Saturday's defeat leaves Liverpool with seven points from their opening five matches, with league leaders Manchester City eight points ahead.