Ross McCormack, Mousa Dembele and Tom Cairney netted for the visitors as Fulham ran riot at Loftus Road.
And the visitors could have won by an even bigger margin had they not taken their foot off the gas.
The two-goal margin was bad enough for Sinclair, though, who summed his reaction to the QPR loss up in two words on Twitter:
Meanwhile, Fulham's Ryan Fredericks teased a QPR fan who said his personal highlight from the game was to mock him.
The Fulham man responded on Twitter after the supporter mocked his appearance.
Next up for QPR is a Championship trip to Bolton Wanderers. Fulham, meanwhile, travel to Blackburn Rovers. There are no prizes for guessing which west London side is feeling more confident right now...