PARIS (Reuters) - France’s former prime minister Alain Juppe is defending a shrinking lead in the race to win the conservatives’ nomination for next year’s presidential election, two opinion polls showed on Thursday.

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Whoever wins the two-round primary on Nov. 20 and Nov. 27 has a strong chance of becoming France’s next president.

Juppe, 71, has for months been favorite. But he has been struggling to fire up voters and has this week been losing some ground to his chief rival, former president Nicolas Sarkozy, and another ex-prime minister, Francois Fillon.

A poll by Cevipof and Ipsos-Sopra Steria showed Juppe scoring 36 percent of votes in Sunday’s opening round of the Les Republicains party primary, five percentage points less than in October. It showed Sarkozy, on 29 percent, would qualify for a head-to-head second round runoff against Juppe a week later.

Juppe was seen beating Sarkozy in the runoff with 57 percent of votes to his rival’s 43 percent, with his lead still comfortable but 3 points smaller than last month.

Fillon, whose potential first-round score has risen 10 points in just one month, has become a possible threat to the frontrunners but was not seen making it to the two-way run-off.

The seven contenders in Sunday’s first round of Les Republicains party primary were set to face off in the last of three televised debates later on Thursday.

Socialist President Francois Hollande is struggling with low poll ratings and has yet to say whether he will run for a second term next spring. The opinion poll confirmed the widely held expectation that the left would be out of contention, and far-right leader Marine Le Pen would be the likely opponent of any center-right candidate in the decisive runoff in May.

The Internet-based survey was based on more than 18,000 voters, with the questions on the primaries narrowed to 1,337 people certain to take part.

A separate Ifop-Fiducial poll for Sud Radio showed Juppe getting 31 percent of votes in the first round of the primaries on Sunday, versus 30 percent for Sarkozy and 27 percent for Fillon.

That poll was carried out online Nov. 10-17 with 744 people certain to vote in the primaries. Juppe’s rating is down 2 points since a survey carried out Oct. 31-Nov. 14, Sarkozy’s unchanged and Fillon up 7 points.

Juppe would win the second round versus Sarkozy with 57 percent of the votes, the poll showed.