MEXICO CITY (Reuters) - The leftist front-runner for Mexico’s presidency has retained his lead ahead of this year’s election while the ruling party hopeful failed to gain traction during the festive season and slipped back slightly, a poll showed on Wednesday.

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Former Mexico City mayor Andres Manuel Lopez Obrador of the National Regeneration Movement (MORENA) had 23.6 percent support in a survey by polling firm Mitofsky for newspaper El Economista, up 0.6 percentage points from a December poll.

Jose Antonio Meade, who is seeking the nomination of the ruling Institutional Revolutionary Party (PRI) for the July election, trailed in third place at 18.2 percent, down 1.2 percentage points from the Mitofsky poll last month.

Meade’s lackluster polling figures could aggravate grumblings among party members that the former finance minister - who is not a PRI member - is failing to energize the campaign, and cannot take his nomination for granted.

The PRI is due to formally elect its candidate on Feb. 18.

Running second in the survey of 1,000 voters was the conservative National Action Party’s (PAN) Ricardo Anaya, who heads a left-right coalition of opposition parties, polling 20.4 percent. That was an improvement of 0.4 points from December.

Mitofsky said the poll had a margin of error of 3.1 percentage points.

Worryingly for Meade, the poll showed that 58.8 percent of respondents said they would never vote for the PRI, up 1.4 percentage points from the previous survey.

By contrast, MORENA and the PAN improved their image among the electorate. Both parties are now rejected by just over 34 percent of voters, according to the survey, which was conducted via face-to-face interviews between Jan. 12 and 14.

Lopez Obrador, who was runner-up in 2006 and 2012, has spent years railing against political corruption and inequality.

The credibility of the PRI, which has dominated Mexican politics for most of the past century, has been undermined by graft, gang violence and accusations of electoral fraud.

Meade has avoided corruption scandals in office and the PRI hopes his selection could detoxify the party’s brand. However, critics contend he has run a timid campaign so far that has done little to set himself apart from the government’s failings.

Putting preferences aside, the poll found that 25.6 percent expected Anaya to win the election, followed by Lopez Obrador with 25 percent, and Meade with 23.7 percent.

The poll also showed that Lopez Obrador was the favored candidate for urban voters, followed by Anaya, while Meade had a substantial advantage over both in rural areas.