8:47 AM PT -- R. Kelly's lawyer Jennifer Bonjean tells TMZ ... "Our fight is not over. We will see review from the USSC (SCOTUS) on the statute of limitations questions at a minimum. And he has habeas remedies at his disposal. And if we win in NY. He will be entitled to resentencing in Illinois. So this story is far from over."

R. Kelly's crusade to make a dent in his lengthy lockup in prison has crashed and burned ... a federal appellate court just upheld his conviction and sentence to cap off the week.

The "Ignition" singer was sentenced to 20 years in prison in his child porn case out of Chicago, and the 7th Circuit Court of Appeals just affirmed that sentence -- this after Kelly tried having it tossed, citing the statute of limitations had passed as his defense.

In reaching its conclusion, the court called Kelly's 30-year sentence from his New York case the "elephant in the room" ... and said the Chicago case sentence was set with that in mind.

According to the court, the sentence also makes sense in light of the "horrible, horrific" nature of Kelly's crimes ... for which Kelly was convicted in 2021.

In his New York appeal, Kelly argued the highly influential "Surviving R. Kelly" Lifetime docuseries influenced the trial before it even got off the ground and he was unfairly painted to be guilty.

But with this ruling out of Chicago federal court, the future may not be too promising for his chances in New York ... but the courts will obviously have the final say.

Time will tell if he has the same luck as Harvey Weinstein -- for now in Chicago, not at all.