A betting market's odds on Brazil's election flipped overnight in a way that has people suspecting foul play, which is bad news for confidence in the vote's legitimacy.

• A prediction market with $33 million riding on the race had one candidate at an 86% chance to win the day before the vote, with Lula far behind.
• That same candidate reportedly won the final debate decisively, which should have helped, not hurt, his odds.
• Instead, the market flipped completely and Lula ended up ahead, a swing commentators compare to a massive underdog upset that defies the pre-vote signals.
• The sudden reversal, with no clear event to explain it, is fueling claims that something was manipulated behind the scenes.

Outlook: Expect continued scrutiny and accusations over the vote's integrity as people look for an explanation for the unexplained flip.