OTTAWA – Prime Minister Stephen Harper’s Conservatives have narrowly retained the late Jim Flaherty’s suburban Toronto seat and easily hung on to another riding in their Alberta stronghold.

But it was Justin Trudeau’s Liberals who – once again – showed all the momentum in two byelections Monday.

The Liberals were the only party to increase their share of the vote in both ridings and the gains were considerable.

Their vote share almost tripled in Whitby-Oshawa, where political neophyte Celina Caesar-Chavannes came within eight points of knocking off the Tories’ Pat Perkins, a high-profile, former two-term Whitby mayor who’d been endorsed by Flaherty’s family and a parade of senior cabinet ministers.

READ MORE: Conservative Pat Perkins wins Whitby-Oshawa byelection

Liberal support in Alberta’s Yellowhead riding, meanwhile, increased almost seven-fold over the paltry three per cent captured in 2011, when the party ran fourth behind the NDP and Greens.

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Liberals have posted gains – some of them dramatic – in every byelection since Trudeau took the helm 19 months ago. Monday’s results helped further cement the perception that the Liberal party is the only one with the wind at its back as federal politicos prepare for a general election in less than year.

“You proved that positive change for Canada is coming soon,” Trudeau crowed at Caesar-Chavannes’ headquarters in Whitby.

“And that it can’t come from a tired old government. Only the Liberal party can bring it.”

READ MORE: Tories coast to byelection win in Alberta, hold Yellowhead riding

While they emerged victorious in both ridings, the ruling Conservatives’ share of the vote was markedly reduced from 2011 – down nine points in Whitby, 15 points in Yellowhead.

NDP support was down slightly in Yellowhead and collapsed in Whitby-Oshawa, continuing the downward trend that has befallen the official Opposition since Trudeau resurrected the Liberal party.

Flaherty, the former finance minister who died suddenly last spring, took Whitby-Oshawa in 2011 with a comfortable 58 per cent of the vote, more than 35-points ahead of his nearest rival, New Democrat Trish McAuliffe.

McAuliffe won a respectable 22 per cent in 2011. She ran again in Monday’s byelection but managed to capture just eight per cent this time.

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The collapse of NDP support in Whitby-Oshawa follows the party’s loss of the downtown Toronto riding of Trinity-Spadina to the Liberals in a byelection last July.

Perkins captured 49.2 per cent of the vote for the Tories while Liberal Caesar-Chavannes took 40.7 per cent – a 26-point jump over the Liberal showing in 2011.

The close result in Whitby, despite an all-out push by the Conservatives, suggests the resurgent Liberals may give the ruling party a run for its money in the crucial suburban ridings around Toronto – a key battleground in next year’s general election.

But despite all the talk of Liberal momentum, a senior Conservative privately noted that the Trudeau Liberals have actually managed to steal away only one seat – Labrador – from the ruling party thus far.

Furthermore, he noted that the Conservatives’ reduced share of the vote in Whitby on Monday was still six points higher than when Flaherty first won the seat in 2006.

Flaherty’s widow, Christine Elliott, said she had “no doubt that Jim would have been very, very happy with this result.”

Elliott, who represents the riding provincially and is a front-runner for the Ontario Conservative leadership, predicted that Perkins will increase her margin of victory over the years, just as her husband did.

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Conservative party spokesman Cory Hann said the byelections prove that Canadians “know Justin Trudeau is high risk and chose instead to support a strong leader for the serious job of prime minister – Stephen Harper.”

The results are also a vote of confidence in the recent spate of tax cuts the Harper government has introduced, including boosting the universal child care credit and income splitting for couples with young children, Hann said.

Voters know they’re better off with Harper’s plan to “balance the budget, lower taxes and create quality jobs” than with Trudeau’s plan to “claw back these tax breaks, increase debt and raise taxes to pay for new expensive national programs we cant afford,” he added.

In Yellowhead, Tory candidate Jim Eglinski, a former RCMP officer and former mayor of Fort St. John, coasted to victory with 62.6 per cent of the vote – miles ahead of Liberal Ryan Maguhn’s 20 per cent and New Democrat Eric Rosendahl’s 9.5 per cent.

Even so, the Conservative margin of victory was reduced from 2011, when Rob Merrifield took the riding with 77 per cent of the vote – a whopping 64 points ahead of the second-place NDP.

Turnout in both ridings was low, as is typical of byelections: 31.8 per cent in Whitby-Oshawa and just 16 per cent in Yellowhead.