Sandra Pupatello, former Windsor West MPP delivers her candidate speech at the Ontario Liberal Leadership convention Saturday January 26, 2013 at Toronto's Maple Leafs Gardens. TARA WALTON/ TORONTO STAR

Brian Masse will need to rely on his personal popularity if he hopes to keep his Windsor West riding in the NDP fold come this fall, suggests a new Mainstreet Research poll for iPolitics.

According to the poll’s results, Masse and Liberal Sandra Pupatello, a former provincial representative for the southwestern Ontario city, are in a dead heat in the riding, with Conservative Henry Lau trailing in third.

Pupatello has not been selected as the Liberal nominee for the riding and as of Aug. 23, there is only one other candidate vying for the nomination alongside her.

But when respondents were asked strictly about their party preferences, the Liberals held a double-digit lead over the second-place Conservatives, while the NDP sank to third place.

Masse, who has represented the riding since 2002, was the preferred choice of 31.8 per cent of respondents in the 468-person phone survey, conducted on Aug. 21.

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Pupatello, who represented Windsor West at the provincial level as an Ontario Liberal between 1999 to 2011, drew the support of 33.1 per cent of voters, while Lau was the top choice of 18.6 per cent. The Green and People’s Party candidates drew 2.6 and 1.7 per cent of support, respectively, with 12.4 per cent unsure about who they would choose.

When excluding undecided voters, Pupatello’s lead over Masse moves to 37.6 to 36.3 per cent, with Lau jumping to 21.3.

The margin of error for the poll is 4.53 percentage points at the 95 per cent confidence level, according to Mainstreet.

Masse won the riding in 2015 with 52.5 per cent, while the Liberals were second at 25.3 and the Conservatives third with 20.8. Pupatello, who served as education minister, among other roles, in Dalton McGuinty’s cabinet in the 2000s, unsuccessfully sought the Ontario Liberal Party leadership in 2013, losing on the third and final ballot to Kathleen Wynne.

When asked strictly about the parties, respondents were far less favourable to the NDP. The Liberals were the top choice of 33.8 per cent of voters, while the Tories were selected by 23.6 and the NDP was preferred by 17.8. The Greens drew 5.1 per cent of support, the People’s Party of Canada had 1.9 per cent, and 17.9 per cent were undecided.

And when the undecided voters were excluded, the Liberal lead over the Tories moved to 40.9-29.2 per cent, while the NDP had 21.4 per cent of support. The Greens moved to 6.2 per cent, while the People’s Party increased to 2.3 per cent.

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NOTE: The People’s Party of Canada and Green Party of Canada have since named different candidates in Windsor West than those tested in the poll.

*This story has been updated to clarify that Pupatello remains a candidate for the Liberal nomination in the riding.