Pupatello, who quit politics in 2011, captured 504 committed first-ballot delegates (27.44 per cent) to the leadership convention in Toronto Jan. 25-27, according to official results released at two a.m. Monday.
Former education minister Kathleen Wynne, who represents Toronto Don Valley-West, was a close second with 463 (25.2 per cent) after a weekend of voting to select 1,837 delegates who will be able to cast ballots for the new Liberal leader.
Former MP Gerard Kennedy, who lost the 1996 leadership race to McGuinty and also lost a 2006 bid for the federal Liberal leadership, was third in the weekend voting with 257 committed delegates (14 per cent), followed by former government services minister Harinder Takhar with 244 (13.28 per cent).
Former labour minister Charles Sousa finished fifth with 198 delegates (10.78 per cent), and former children's services minister Eric Hoskins finished in last place with 104 (5.66 per cent).
About 44,000 Liberal members, most of whom were signed up by the candidates after McGuinty's surprise resignation Oct. 15, were eligible to vote to elect 16 delegates from each of the 107 ridings. Delegates were also elected from Liberal campus group's and women's clubs.
Voting was held Saturday and Sunday in different regions of the province, with Pupatello maintaining a lead both days with Wynne always a close second.
The weekend results were the first real confirmation that the two women are the front-runners in the leadership race, with just two weeks to go to the convention.
There were also 67 delegates elected as independents, many of whom had supported former Winnipeg mayor Glen Murray until he dropped out of the race last Thursday to support Wynne.
The delegates will be joined by about 600 former MPPs, MPs, party executives and other "ex-officio" Liberals eligible to vote for the new leader, who will automatically become Ontario's next premier.
As with the delegate selection results, Pupatello had the most high-profile endorsements and support among her former Liberal caucus and cabinet colleagues heading into the weekend, followed by Wynne.
Pupatello, who served alongside McGuinty in opposition and in the last government as minister of economic development and trade, did not seek re-election in 2011 when the Liberals were reduced to a minority, and like Kennedy she does not have a seat in the legislature.
She has promised to recall the legislature as soon as possible and said she will run in a byelection rather than calling a general election in 2013. Finance Minister Dwight Duncan has offered to give up his Windsor seat for Pupatello if she wins the leadership.
The race was triggered by McGuinty's surprise resignation and decision to prorogue the legislature until a new Liberal leader was selected, which also killed hearings set to begin the next day into the decision to cancel two gas plants in government-held ridings at a cost of at least $230 million.
The scandal over the gas plants, a nasty battle with teachers over wage freeze legislation and a police probe into irregular activities at the province's Ornge air ambulance service added up to a very difficult year for the Liberals, and Pupatello said it's helpful that she was not in government during that time.
"Party members are telling me this, that’s what their perception is, that’s how they feel I would have an advantage because I wasn’t in the House, I didn’t vote on these controversial bills," she told The Canadian Press in an interview Friday.
The Liberals have "a lot of making up to do on a number of fronts before the public wants to trust us with their taxpayers’ money," added Pupatello.
"Inside the party, everywhere we go, we are getting a very warm reception, which is how you know it’s really unlike the general public right now," she said.
Wynne, a former Toronto school trustee who was first elected to the legislature in 2003 and also served as transportation minister and minister of aboriginal affairs, said her homosexuality has come up "as an electability issue" in every campaign, but isn't a deciding factor.
"In every election homophobia has been part of the landscape and in every campaign I’ve been able to become connected enough to my constituents that they know who I am and that I can be elected on my merits," she said in a recent interview.
"I really believe that it underestimates Ontarians to assume that sexual orientation or gender or race or background are going to be the determining features."