It was the ninth sending off of the controversial midfielder's career - with referee Anthony Taylor having little option but to show red when Barton struck Tom Huddlestone with a cheap shot below the belt.
Barton apologised to his team-mates and the travelling Rangers fans following the 2-1 defeat but insisted he was attempting to support Furlong, whose full-blooded challenge on Nikica Jelavic set events in motion.
Furlong was eventually booked but Barton, who also raised his arm to push Alex Bruce, felt Hull's players were attempting to have the 19-year-old sent off.
"I'm gutted I got sent off. I've let my team-mates down today and being someone who puts the team above everything else I'm gutted about that," he posted on Twitter shortly after full-time.
"Young kid making his debut has made a good tackle. Couple of Hull players trying to get him sent off. My job as captain is to protect him.
"I've tried to prevent Hull's players influencing referee as u can see by me pushing Bruce away.
"I've apologised to the lads and would like to apologise to all QPR fans who travelled today.
"My actions towards Huddlestone were certainly not malicious, it was a stupid reaction to being barged but I can appreciate it wasn't right."
Prior to the latest episode in Barton's hall of shame, he had been booked in his seven previous matches - a Premier League record.
But new manager Chris Ramsey declined to hang his skipper out to dry.
Ramsey will discuss the issue with Barton, but only once he has a chance re-watch the moment with fresh eyes.
"It's an incident we probably wouldn't want to happen," he said.
"It's always difficult when you have players who have that bit of edge, and trying to get their emotional control is the thing we need to get under wraps.
"I'm sure if the incident isn't a good one when we review it, Joey will be the first one to put his hand up and admit that he probably should have acted in a different manner.
"I would rather look at it in the cold light of day when tempers and emotions have calmed down, then discuss it with the player at that point."
Asked if Barton's suitability to wear the armband was now in doubt, Ramsey was unequivocal.
"No. There's no question over it," he said.
Steve Bruce offered a colourful take on Barton's indiscretion, stating: "You can't go punching people in the knackers, can you?
"Unfortunately when the red mist comes we've all done stupid things. It was one of those silly moments unfortunately."
Bruce was magnanimous to QPR striker Charlie Austin, who cancelled out Jelavic's opener with a fine header then celebrated by clutching his knee.
That was a clear reminder to the Tigers of their questionable decision to pull out a deal for Austin in 2013 due to a failed medical.
But Bruce, buoyed by Dame N'Doye's 89th-minute winner, was full of praise for the one that got away.
"I congratulated Charlie for the way he's handled himself after what happened here because it wasn't easy," he said.
"He showed the manner and dignity of a proper man because it couldn't have been easy. He didn't even know he had a bad knee at the time.
"But he's certainly a proper centre-forward and our loss is definitely QPR's gain."