(Adds details, polls close)
By Alexandra Alper
SAN JOSE, Costa Rica, April 6 (Reuters) - A center-left academic who campaigned on a popular anti-corruption message and has never been elected to office is expected to win Costa Rica's presidential run-off on Sunday after his opponent slid in polls and stopped campaigning.
Luis Guillermo Solis, a former diplomat, rode a wave of anti-government sentiment over rising inequality and graft scandals to finish ahead in February's first-round vote, when pollsters had predicted he would come in fourth.
Facing a depleted war chest, rival Johnny Araya of the ruling National Liberation Party (PLN) quit campaigning after an opinion poll showed him trailing badly. However, Araya remains on the ballot as stipulated by the constitution and his party continued to campaign, so theoretically he could win.
Polls closed at 6 p.m. (midnight GMT), and first results are expected to be announced later on Sunday.
Solis has promised to fight Costa Rica's stubborn poverty rate while stamping out corruption, an issue that has dogged incumbent President Laura Chinchilla's administration.
"There's been so much abuse of power and the people are sick of it," said 63-year-old street vendor Raul Cabrera, who voted for Solis' Citizen Action Party (PAC) before polls closed. "There are too may people without work."
Local media said turnout was low but some reported a pickup in the afternoon. Solis urged those who stayed away to come and help push him over the finish line.
Red-and-yellow PAC flags fluttered from the windows of cars crisscrossing San Jose throughout the day. A handful of Araya supporters drove past with discreet green-and-white bumper stickers that read simply 'Johnny', a muted display after the glut of banners and confetti seen in the first round.
None of the candidates won more than 40 percent of the votes in February to avoid a run-off, paving the way for Sunday's showdown.
Voters appear eager to elevate the young PAC to its first presidential victory and wrest power from the PLN, which has been in power since 2006.
A prosecutor's investigation into allegations of abuse of authority and embezzlement while Araya was mayor of San Jose made it hard for the former front-runner to distance himself from party scandals.
Despite ending his campaign early, Araya said he would be happy to govern if he were to win the vote.
A University of Costa Rica survey last month showed Solis had more than 64 percent support while Araya trailed with around 21 percent. Within hours, Araya shelved his campaign.
Solis, 55, campaigned on a pledge to eradicate corruption and help the poorest.
"We want to recover that sense of solidarity, of social inclusion, and commitment to the neediest Costa Ricans that has been lost," he told a news conference on Saturday.
Solis, however, faces hurdles of his own.
Threatened by the low turnout typical of second-round voting and the looming challenge of a divided Congress, Solis could end up with a weak mandate. His PAC will have just 13 of the 57 seats in Congress.
Solis has also said he will wait two years before raising taxes despite promises to boost social spending.
"He's going to have a government without money, a fiscal deficit of 6 percent, and lots of social spending commitments," said Jose Carlos Chinchilla, a political analyst and a director at the University of Costa Rica.
Solis has said he hopes to attract new businesses to Costa Rica's booming free-trade zones, which have enticed the likes of Hewlett-Packard Co. (Additional reporting by Zach Dyer; Editing by Simon Gardner, Gabriel Stargardter, Steve Orlofsky and Mohammad Zargham)