In a win for the generic drug company Teva Pharmaceuticals USA Inc. and its lawyers at Winston & Strawn, an appeals court has knocked out a Bristol-Myers Squibb Company’s patent on the Hepatitis B drug Baraclude.

In a 20-page decision issued on Thursday, the U.S. Court of Appeals for the Federal Circuit ruled that BMS’s patent on the compound entecavir, marketed as Baraclude, is invalid on obviousness grounds. The ruling, which affirms a lower court decision, paves the way for Teva to launch a low-cost generic version of the drug, which pulled in $314 million in U.S. revenue in 2013. In a press release, Teva said it plans to launch its generic as soon as it receives approval from the U.S. Food and Drug Administration.

The oral argument pitted against each other two high-profile Federal Circuit advocates, George Lombardi of Winston & Strawn for Teva and William Lee of Wilmer Cutler Pickering Hale and Dorr for BMS. Historically, Winston & Strawn has handled more patent work for generic drug companies than any other firm. The other Winston partners representing Teva include Lynn Ulrich, Ivan Poullaos, and Julia Mano Johnson.

BMS commenced the case in 2012 after Teva applied for FDA approval to market the generic version of Baraclude in 2010. Following a bench trial, U.S. Magistrate Judge Christopher Burke in Wilmington, Del. invalidated the patent for Baraclude on the grounds that it would have been obvious to scientists to use the compound patented by MBS. The ruling wasn’t a total loss for BMS, however, because the judge rejected Teva’s argument that there’s clear evidence that the inventor of BMS’s patent tried to dupe the patent office into issuing the patent.

The only issue on appeal was Burke’s obviousness ruling. In Thursday’s decision, penned by recently appointed Chief Judge Sharon Prost, the court held that, “based on there prior art and testimony, the district court properly found strong evidence of obviousness.”

The ruling will not have a real meaningful impact on Teva and BMS’s bottom lines. As FiercePharma explained here, the patent at issue expires in 2015, so Teva would have been free to launch its generic version of Baraclude then, regardless of the court case’s outcome.