/In Caracas' 23 de Enero barrio, a mural of 20th-century rebel icon Ché Guevara overlooks a bust of Simón Bolívar, the 19th-century Latin American independence hero idolized by left-wing 21st-century Venezuelan President Hugo Chávez. All three men appear on many of the slum's walls — even in a fresco depicting Chávez as the protagonist of The Last Supper, breaking bread with leftist legends like Karl Marx and Fidel Castro. Here, Chávez's opponents are usually known as "los esquálidos" — the "squalid" bourgeoisie. Yet on Sunday, Feb. 12, as millions of Venezuelans voted in a unified primary election to choose which candidate will represent opposition parties in the Oct. 7 presidential election, that animosity seemed relatively muted.

In fact, beneath those same murals, a surprising number of 23 de Enero locals lined up to vote for a challenger to Chávez, who after 13 years as President and Latin America's radical leftist standard bearer is seeking another six-year term. "Chávez has only one idea," said a nearby fruit vendor, Roberto González, 64, chopping a purple malanga as he talked about Chávez's socialist revolution. "We need various ideas, because that's democracy." At the end of the day, the opposition's decisive choice was Henrique Capriles Radonski, 39, a centrist state governor who won 64% of the vote, double that of his closest rival. But Capriles' landslide victory wasn't the only striking result. The turnout of more than three million voters, more than half of Venezuelans who identify with the opposition, far surpassed analysts' expectations.

All of which seems to confirm that Chávez, who announced last summer that he is battling cancer, is also facing his toughest electoral test yet. For the first time since the former army paratrooper officer toppled Venezuela's corrupt political establishment in the 1998 election, his once hopelessly incompetent rivals have managed to galvanize and mobilize voters who are questioning his handling of the economy (a 26% inflation rate), violent crime (one of the western hemisphere's highest murder rates) and his polarizing, sometimes authoritarian style. "This is an excellent start for Oct. 7," says María de Oteyza, spokesperson for the Unified Democratic Panel, or MUD, the opposition party alliance. "It was a resounding success." Luis Vicente León, head of the independent Caracas polling firm Datanálisis, agrees. "Capriles begins [his campaign] legitimized," says León. "The primaries have created great momentum for him."

Maintaining that momentum will be Capriles' biggest challenge, especially against a President who is still Venezuela's most popular political figure. "The future of Venezuea won today," Capriles, the Governor of Miranda state adjoining Caracas, declared at a victory rally Sunday night, backed by fireworks and thousands of cheering supporters. But though one credible poll last summer showed Capriles nearly tied with Chávez, more recent surveys put him some 20 points behind. And while Capriles should get a significant poll bounce from his primary triumph, the reality is that he's up against an incumbent who controls the hemisphere's largest oil reserves as well as a formidable state-run media and patronage apparatus.

Still, Capriles' margin of victory seemed to rattle the Chavistas a bit. "We have to determine if those numbers really exist," said National Assembly President Diosdado Cabello of Chávez's United Socialist Party (PSUV). Perhaps the most encouraging sight for Capriles Sunday night, however, was the appearance of his primary opponents onstage with him in an unabashed show of unity. One of them was Leopoldo López, a young and popular former Caracas borough mayor who quit the race last month and threw his support behind Capriles. Just as important, second-place finisher Pablo Pérez, who represents one of the old establishment parties but whose support for Capriles will be as critical as López's, stood alongside them. "If we don't unify," Capriles recently told TIME, "then it's game over."

Capriles has a tough balancing act ahead. He's smart enough to understand that too much direct confrontation with Chávez will alienate many voters who, even if they're looking for change, want to avoid sudden, jarring transformation. As a result, he's emphasizing a conciliatory tone in his campaign and platform, which intends to meld Chávez's popular socialist programs with a more dynamic capitalism. Should he win, for example, he says he does not plan to overturn Chávez's numerous property and business expropriations overnight, but will look at them on a case by case basis. But though Capriles usually refrains from mentioning the President by name, there is little doubt whom he's targeting when he describes Venezuela as a "country in crisis" with a "government that pretends Venezuela has one political color."

Meanwhile, Chávez's crimson-colored political machinery has begun whirring to meet the opposition threat. Boris Segura, an analyst at the New York investment bank Nomura, estimates government spending has shot up 56% in the first two months of 2012, compared to the same period last year. That largesse, fueled by $110-a-barrel oil prices and Latin America's biggest bond issuance last year, is being channeled to social programs that include new, $100-a-month stipends for poor children, $350-a-month pensions for low-income senior citizens and myriad other dole projects that the President's critics, of course, claim are simply vote-buying measures. "It's an unequal fight," Capriles told TIME. "It's an abuse of power."

Whether or not that's the case, they're what keeps most 23 de Enero voters on Chávez's side of the walls. "I never had the opportunity to study when I was young," says Jesús Matina, 60, buying fruit from vendor Rodríguez. "Thanks to Chávez I made it to university." Capriles has the daunting task of winning over millions like Matina if he hopes to make it to Oct. 7 and win.