Klopp lamented the errors that led to Marcus Rashford's double inside 24 minutes at Old Trafford, but felt his side's second-half performance could have brought a draw.
Following the 2-1 loss at Old Trafford, Liverpool trail second-placed United by five points with eight games remaining in the battle for the runners-up spot.
Asked about Rashford ahead of United's Champions League clash with Sevilla on Tuesday night, Mourinho said: 'I read something, some quote from the worst manager in the history of the Premier League - Frank De Boer.
"But in the moment I can not, and I don't want to, think about anything else".
'How can I be frustrated if don't create a lot of chances against a world-class team like United, ' he said.
They're down to fourth in the table, five points behind United in second, and looked largely ineffective on Saturday against their rivals. "The more you do, the easier the results come on the pitch".
"We have to defend these situations better". We would have more points and it would change my life massively.
Rashford has made 27 league appearances this season, coming off the bench 13 times.
The Reds conceded both their goals in nearly identical positions as twice Dejan Lovren was bullied off the ball by Lukaku and Rashford made Klopp's team pay for their mistakes as he took both his goals superbly.
"With Romelu Lukaku, he can win the headers sometimes - we did it afterwards [won the headers], but in these two situations we didn't".
Swansea City, who had Jordan Ayew sent off in the 11th minute, held Huddersfield Town to a 0-0 draw at the John Smith's Stadium while Wayne Rooney's penalty miss mattered little as Everton beat Brighton and Hove Albion 2-0 at Goodison Park.