"It's difficult to find an explanation for the first 20 minutes," Farke told a press conference.
"We lacked the basics. The basics are to run, to fight, to invest, to be brave, to be compact as a team. We were lacking this in the first 20 minutes."
Leeds were lacklustre, suffering their heaviest defeat of the season as QPR scored two goals before the midway point in the first half, followed by two set-piece goals after the break.
Farke was full of praise for opposition QPR and promotion rivals Leicester, who are now guaranteed a top-two finish in the second-tier Championship and a place in next season's Premier League.
Ipswich Town, who are now favourites to join Leicester in the other automatic promotion spot, sit one point behind Leeds in third with two games in hand. They face Hull City on Saturday.
"Congratulations to QPR for a well-deserved win tonight and congratulations to Leicester for promotion," said Farke.
"Right now it's not in our hands anymore. The race is not over. If Ipswich don't win the next two games we have a lot to play for on the last day."
Leeds host fourth-place Southampton on the final day of the season, who themselves lost 5-0 to Leicester earlier this week.
Rangers manager Marti Cifuentes was full of praise for his own side, who secured their status in the Championship having been in danger of relegation before kickoff.
QPR were mired in the relegation zone, six points adrift of safety, when they appointed Cifuentes in October but after taking 45 points from 31 games, Cifuentes has guided his team to safety with one game to spare.
"When I came here I was perhaps a bit crazy thinking I was sure we could make the great escape. I think we managed it," Cifuentes said.
"Tonight is going to be a long night for a lot of people."
