The U.S. Court of Appeals for the Second Circuit on Tuesday rejected a Brazilian sugar cane magnate’s last-ditch effort to vacate $120 million in arbitration awards against him. Adriano Giannetti Dedini Ometto had argued that the award should be tossed because the arbitration panel’s original chairman, David Rivkin of Debevoise & Plimpton, didn’t disclose that his colleagues at Debevoise worked on deals involving Ometto’s adversary in the case.

The dispute stemmed from a soured sugarcane deal in 2007 between Ometto and the Spanish biofuels company Abengoa Bioenergia Agricola Ltda., known as Abengoa. Abengoa alleged in two International Chamber of Commerce arbitrations in New York that Ometto misrepresented aspects of the sale of his sugarcane businesses. In 2011, with help from Iñigo Quintana of the Madrid firm Cuatrecasas, Gonçalves Pereira, the company won two awards totaling roughly $120 million.

Ometto, looking to a New York team from Hogan Lovells, petitioned the ICC to vacate the awards, arguing that Debevoise’s Rivkin improperly served as lead ICC arbitrator without disclosing that his firm was advising on three deals in which Abengoa was a counterparty. Rivkin resigned, but a reconstituted panel reconfirmed the awards.

Ometto also sued to vacate the awards in U.S. district court in Manhattan. Under U.S. law, federal courts may upend an arbitrator’s findings only in cases of “evident partiality,” but the federal appellate courts have applied that standard in different ways. Ometto cited Ninth Circuit precedent in arguing that the awards should be tossed, but U.S. District Judge Jed Rakoff refused, siding with Abengoa in his decision last January. Rakoff reasoned that to vacate the awards in New York, a “reasonable person would have to conclude that an arbitrator was partial to one side.” In this case, he noted, Rivkin only became aware of the potential conflicts after the awards were issued.

Before accepting his appointment as a lead arbitrator in the case, Rivkin had requested a conflicts check on the parties. When nothing flagged Abengoa as a firm client or counterparty, Rivkin then opened up a new client matter, but he listed only Ometto and an Abengoa subsidiary, ASA Bioenergy Holding A.G., not the parent Abengoa. Because of that omission, and because the firm’s system didn’t retain Rivkin’s earlier conflicts search, Debevoise partners subsequently took on three new Abengoa-related matters without knowing about the potential conflict—and Rivkin was never alerted. (The firm says it has since improved its conflicts system.)

In Tuesday’s decision affirming Rakoff, the Second Circuit noted that Debevoise’s conflicts checks system, and Rivkin’s omission, left something to be desired. But the court found no error in Rakoff’s decision. “To the extent that the lead arbitrator was careless, that carelessness does not rise to the level of willful blindness,” the Second Circuit panel wrote.

“This is consistent with U.S. legal policy on arbitrations, that awards are not to be toyed with lightly,” said Shearman & Sterling’s Henry Weisburg, who was tapped by Abengoa to defend the award before the district and appellate court.

Dechert’s G. Eric Brunstad Jr., handled Ometto’s Second Circuit appeal. We called Brunstad to ask whether his client planned further appeals but didn’t immediately hear back.