Janaina Riva leads the implied probability for second place in Mato Grosso’s October 4 Senate contest, where voters select two senators. Multiple polls since July, including MT Dados, Paraná Pesquisas, and Real Time Big Data, show ex-governor Mauro Mendes dominating first-preference votes while Riva consistently tops or shares the lead in second-preference and consolidated tallies, reflecting her profile as a three-term state deputy, MDB state president, and candidate with broad name recognition. The remaining field of nine registered contenders—including José Medeiros, Pedro Taques, and Carlos Fávaro—remains fragmented below 20 percent in most surveys, with elevated undecided and null responses leaving limited room for late consolidation. No major polling shifts or campaign events have altered this ordering in recent weeks.