GUATEMALA CITY - Conservative Alejandro Giammattei could make it fourth time lucky in Guatemala's presidential runoff on Sunday if misgivings about his opponent among urban voters outweigh her support in the Central American nation's poor Mayan highlands.

Whoever takes office in January will face a testy relationship with U.S. President Donald Trump, who last month strongarmed the outgoing government into signing an agreement that will turn Guatemala into a buffer zone for U.S.-bound migrants.

Giammattei and his center-left rival, former first lady Sandra Torres, both criticized the deal, but Trump's threats of economic sanctions are unlikely to leave either of them much room to maneuver if the next administration does not honor it.

Potentially complicating such tough decisions, neither candidate is hugely popular.

Torres, 63, has high negative ratings in the densely populated urban areas, in part because of her connections to an investigation being conducted into alleged illicit electoral financing in a previous campaign.

Her base is in rural areas such as the highlands where she is remembered for social programs during her former husband's administration.

Turnout is expected to be on the low side and the winner is unlikely to command a strong mandate, especially after electoral authorities excluded other popular candidates from the first round in June - conservative candidate Zury Rios on the grounds that close relatives of coup leaders are barred from top office, and anti-corruption crusader Thelma Aldana due to an arrest warrant against her in a corruption case that supporters said was trumped up.

A former prisons director who himself spent a few months behind bars, Giammattei got barely 14 percent of the vote in the first round with a tough-on-crime message, and his Vamos party won just a smattering of seats in Congress.

Giammattei's prison time was linked to an investigation into extrajudicial killings, but he was later cleared.

Torres' National Unity of Hope had the strongest showing in Congress but also fell well short of a majority.

A CID-Gallup opinion poll of 1,216 voters in conducted between July 29 and August 5 gave Giammattei the advantage going into the run-off, with 39.5% support, compared to 32.4% for Torres. The poll has a margin of error of 2.8 points. -Reuters