Mexican presidential front-runner Enrique Pena Nieto has extended his lead as support for the ruling party candidate weakened, an opinion poll showed on Monday.

The voter survey by polling firm Buendia & Laredo for newspaper El Universal showed backing for Pena Nieto, candidate of the opposition Institutional Revolutionary Party (PRI), at 41.6 percent, down from 42.5 percent in a poll published on March 26.

However, support for Josefina Vazquez Mota, candidate of President Felipe Calderon's conservative National Action Party (PAN), dipped to 17.5 percent from 23.7 percent in the last survey, thereby increasing Pena Nieto's effective advantage.

Leftist hopeful Andres Manuel Lopez Obrador, the runner-up in the 2006 election, was at 16.4 percent, compared with 16.9 percent in the March poll.

(Reporting by Dave Graham; Editing by Mark Heinrich)