Leeds 28 Harlequins 16
Coach Brian McDermott blamed Harlequins' slow start for their fourth straight engage Super League defeat.
Quins rallied in the second half after trailing 20-4 at the break at Headingley on Friday night.
"Going 12 points down so early was always going to make it difficult for us," said McDermott.
"I thought we did enough to win the match, but Leeds were outstanding near their own try-line.
"There is a lot of character in our side and the boys are devastated because it's our fourth straight loss."
Danny McGuire and Brent Webb scored two tries each for Leeds, with Kevin Sinfield kicking six goals.
Chris Melling scored Quins' only first half try, with Matt Gafa going over by the second.
But by the time of Paul Sykes' late consolation, it was a case of too little, too late for McDermott's men.
Harlequins: Melling, A Smith, Sykes, T. Smith, Gafa, Orr, McLinden, Grayshon, Randall, Heckenberg, Purdham, Hopkins, Paul. Replacements: Rinaldi, Mills, McCarthy-Scarsbrook, Temata.
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