Leftist front-runner Andres Manuel Lopez Obrador of the National Regeneration Movement (MORENA), gestures during the 16th National Tourism Forum at the Chapultepec Castle in Mexico City, Mexico May 7, 2018. REUTERS/Carlos Jasso

MEXICO CITY (Reuters) - Mexican leftist Andres Manuel Lopez Obrador’s lead over his nearest rival narrowed slightly ahead of the July 1 presidential election, a poll by GEA-ISA showed on Thursday.

Lopez Obrador, the former Mexico City mayor, received 29 percent support in the poll conducted from April 28-30, up from 28 percent in a mid-March poll. The results did not strip out undecided voters, unlike a number of polls.

His lead over second-placed Ricardo Anaya, who heads a right-left alliance, fell to five percentage points from six in the prior poll. Anaya’s support rose to 24 percent from 22 percent following the first television debate.

Lopez Obrador, making his third bid for the presidency, has led polls for months, capitalizing on frustration with sluggish economic growth, widespread corruption and rising violence in Latin America’s No. 2 economy.

Jose Antonio Meade, the candidate of the ruling Institutional Revolutionary Party (PRI), remained in third place, holding steady at 20 percent.

The poll adds to other recent surveys that showed Anaya gaining some ground after the debate, during which he portrayed himself as the only alternative to Lopez Obrador.

Independent Margarita Zavala rose one point to 4 percent and Jaime Rodriguez, a maverick state governor who also is running without a party ticket, was steady at 2 percent.

The poll showed 21 percent of voters were undecided, down from 25 percent in the prior poll.

GEA-ISA surveyed 1,070 registered voters in face-to-face interviews, and said the poll had a margin of error of three percentage points.