VANCOUVER -- Liberal leadership hopefuls sparred Sunday over an existential issue for their once mighty party: can it win the next election on its own or does it need to join forces with other progressive parties?

The issue of electoral co-operation produced the only real sparks during the first of five leadership debates, at which federal Liberals got their first chance to directly compare and contrast the nine candidates promising to lead their party out of the political wilderness.

It was a relatively civil affair, with no real punches thrown but a few veiled jabs at front-runner Justin Trudeau over his inexperience and alleged lack of intellectual gravitas.

However, the number of candidates and a format that dwelled repetitively on only a few issues gave Trudeau's lesser-known rivals little opportunity to really make their mark or narrow the Montreal MP's perceived lead.

All nine ruled out a merger with the NDP. Indeed, eight of the nine insisted the Liberals, reduced to a third-party rump in the last election, need no outside help at all to rebound in 2015.

Vancouver MP Joyce Murray alone embraced electoral co-operation, touting her plan to let Liberals join forces with New Democrats and Greens in ridings where a united front could defeat the ruling Conservatives in the next election.

She said it would be a one-time initiative aimed at replacing the Tories with a progressive government that would implement electoral reform, ending the current first-past-the-post system that results in parties winning majorities with less than 40 per cent of the vote.

"Canadians want politicians to work together, they don't like the toxic atmosphere that can be seen in Parliament," Murray maintained.

While there seemed to be some appetite for the idea among the roughly 900 Liberals in attendance, none of Murray's rivals embraced the notion.

Trudeau questioned how electoral co-operation would work.

"What kind of values are we willing to jettison?" he asked.

Arguing that Liberals favour freer trade while New Democrats oppose it, Trudeau said: "I'm not willing to give up our values for that."

Even as they ruled it out, a number of candidates expressed empathy for frustrated progressive Canadians who see electoral co-operation as the only sure-fire way to defeat Prime Minister Stephen Harper.

"There's no doubt that there isn't a person in this room who doesn't understand the frustration -- and the temptation -- of doing something like that," said former Toronto MP Martha Hall Findlay.

But, calling herself a "proud Liberal," she appealed to Liberals to have confidence in their own ability to defeat the Tories.

"Where did our confidence go? The answer for us ... is to once again prove, not just talk about but prove to Canadians that we are the true alternative."

Montreal MP Marc Garneau, Canada's first astronaut, said Harper and NDP Leader Tom Muclair share the same goal of crushing the Liberals in the next election.

"We are Liberals. We are not members of the NDP. We are different than other parties, " he declared. "I will not be an accomplice in this."

Former cabinet minister Martin Cauchon argued that the Liberal party is "unique," a non-doctrinaire, pragmatic, centrist party.

"So, let's protect that great institution that we have and everything outside that today, it is pure distraction."

But Murray stuck to her guns.

"Despite all of the wonderful words about the Liberal party, which I agree with, and despite all of the enthusiasm and confidence that this time we can be government again, which I hope is true, Canada is too important to let Stephen Harper win the election in 2015," she said, sparking spontaneous applause.

"We have got to get rid of Stephen Harper ... We (must) appeal to the 18 million Canadians who did not vote for the Conservatives."

The debate marked the first chance for dark horse candidates to try to narrow the huge lead Trudeau is widely thought to have in the race.

Hall Findlay and Garneau stressed their experience and policy depth, indirectly drawing a contrast with the relatively light resume of the 41-year-old Trudeau, eldest son of late Liberal prime minister Pierre Trudeau and the party's undisputed celebrity.

"There are no silver bullets," Hall Findlay asserted. "We need leadership that is substantive, experienced and intelligent and has the courage to stand up for what we believe. That's why I'm running because that's who I am."

Garneau, a former naval officer, engineer and astronaut, maintained that the party is at a crucial juncture and needs a strong leader.

"Leadership is the product of your life experience, it's what you've done, it's what you've accomplished, it's having a proven track record," he said.

For his part, Trudeau ignored the veiled jabs and emphasized his own strength: his ability to excite average Canadians, particularly heretofore disengaged young people.

"It's not enough for us to sit back and say, 'These are our ideas, come back to the party.' We have to get out and connect with Canadians. If we're going to earn the trust of Canadians once again to govern this extraordinary country, it'll be by engaging with them, town by town, community by community."

For the clutch of lesser-known, never-elected candidates -- Toronto lawyers George Takach and Deborah Coyne, Ottawa lawyer David Bertschi and retired military officer Karen McCrimmon -- the debate offered their best chance to date to demonstrate that they should be considered serious contenders.

While they all claimed to have done just that, Takach argued that there's still plenty more time to make his mark before a new leader is announced on April 14.

"Three months is an eternity in politics," he said.