TORONTO -- Premier Kathleen Wynne was on the defensive from the start of the only leaders' election debate Tuesday, forced to apologize repeatedly for the gas plants scandal and defend soaring electricity rates.

Wynne said voters have a right to be angry over the $1.1 billion the Liberals spent to cancel two gas plants prior to the 2011 election, admitting "the public good was sacrificed for partisan interests."

She said there had been a breach of trust between her government and the people, and vowed it wouldn't happen again.

NDP Leader Andrea Horwath said the Liberals betrayed voters and wasted billions of dollars, calling corruption the central issue of the election campaign.

Horwath said the change from former premier Dalton McGuinty to Wynne doesn't matter because "corruption in the Liberal party runs deep."

Progressive Conservative Leader Tim Hudak said the Liberals cancelled the gas plants just to save seats in the last election, and raised other scandals at eHealth Ontario and the Ornge air ambulance service.

Hudak had to defend his plan to cut 100,000 public sector jobs while also promising to create one million new jobs over eight years, with both Horwath and Wynne accusing him of bad math.

With all three leaders talking over each other at times, Horwath said voters "don't have to chose between bad ethics and bad math."

The leaders faced a total of six questions from voters, starting with a question for Wynne about why the Liberals should be trusted with workers' money for a new provincial pension plan given the waste at the gas plants.

The next questions focused on Ontario's high electricity rates and on the math behind Hudak's million jobs plan.

The party leaders were greeted by cheering supporters as they each arrived at the CBC Broadcast Centre in downtown Toronto for the 90-minute debate.

Five things you need to know about the debate:

1. Gas plants scandal

The Liberal government's decision to cancel two gas plants ahead of the 2011 election was front and centre at the leaders' debate. Progressive Conservative Leader Tim Hudak and New Democrat Leader Andrea Horwath pressed Premier Wynne to explained why she went along with the government decision, which could end up costing taxpayers $1.1 billion. Wynne apologized several times and said she's taken action to make sure that the same mistake doesn't happen again. Both Hudak and Horwath said the Liberals can't be trusted, with the NDP leader saying "corruption runs deep" in the Liberal party.

2. Million Jobs pledge

Hudak made a bold pledge during the debate: He would resign as premier if doesn't keep the promises in his Million Jobs Plan. Hudak later told reporters that he would step down if he did not eliminate the deficit in two years and that he would balance the books even if the province was hit by another recession.

3. Bad Math

Although Hudak came frequently under attack from the other two leaders over the math behind his plan to create one million jobs over eight years, voters who have not followed the election campaign closely would have been left in the dark about the questions raised by some economists. Horwath said the Tory Million Jobs Plan had "a million mistakes in it," while Wynne asked Hudak to apologize for the bad math but neither provided any details.

4. Transit and Transportation

Hudak tried to portray the Liberals as a party that only caters to the urban centres, mostly the Greater Toronto Hamilton Area. Hudak said Wynne's government was pitting one part of the province against the other and promised his party would be fair and make sure that small town Ontario would prosper alongside big cities such as Toronto, Hamilton and Ottawa.

5. Leaders' performance

Despite claims by all three parties that their leaders had won the debate, political observers said they were not impressed with their performance. They said all three leaders missed good opportunities to highlight their platforms or go after their rivals' controversial election promises. The observers said that for the average undecided voter there wasn't much to take away from the debate.