Wynne was making six campaign stops Wednesday in Toronto, five of them in NDP-held ridings.
Horwath said it was a sign the Liberals were straying from their main goal, which is to keep the Progressive Conservatives from coming to power.
"I don't know whatever happened to the Liberals who wanted to stop (Tory Leader Tim) Hudak," Horwath said in Mississauga. "I guess they've given up on that task, but New Democrats have not given up on that task."
Wynne, however, insisted she was the only who could prevent Hudak from being elected.
"If people don't vote for our plan, then Tim Hudak will be the premier, because it is a tight enough race that that is what will happen," Wynne said.
"If you want a progressive government, you want a progressive plan that presents opportunity and security for the people of Ontario, that's the Ontario Liberal Party," she said.
A senior Liberal campaign source said they're trying to drive home the point that there are only two choices in the election: the cuts proposed by the Tories or the progressive measures the Liberals put in their budget, a message that resonates with NDP supporters.
"As we drive this kind of choice between these two options, we need to win over people who in the past have voted NDP," the source said.
"We need to win them over in seats that are currently held by the Conservatives or the Conservatives are challenging us in, in order to ensure that there's not a margin of defeat. And also we need to go to ridings that have been traditional NDP ridings, because a lot of NDP voters are very frustrated and very disappointed with the course that the party has taken in this election, including triggering the election in the first place."
Horwath suggested she isn't concerned that Liberals will take those Toronto seats from New Democrat incumbents.
"We have very strong MPPs and very strong ridings," she said. "No matter what the Liberals say the only way to get strong voices in downtown Toronto on the issues that are important to Torontonians is to make sure those hard-working NDP MPPs are there."
Horwath herself spent the last day of the campaign swinging through eight ridings, none of which are currently held by the NDP.
She made stops around the Greater Toronto Area — the NDP hopes to pick up another seat in the area surrounding the city after they nabbed their first-ever seat in that area in 2011 — and eastern Ontario.
Horwath's last stop of the day was with federal NDP Leader Thomas Mulcair, who made his first public appearance of the campaign alongside the provincial leader.
"Since the beginning of this campaign, we've been doing the same thing, going across the province," he said to a crowded bar in Kingston. "Andrea's had a positive plan, a message of hope of what we can accomplish together...Meanwhile, the Liberals have been crossing the province attacking the NDP."
Horwath has joked that the strategy on the last day seems to be to exhaust the leader, though she noted many of her campaign days have been jam-packed.
"It's not like I've been slacking off over the last couple of days," Horwath said.
Ontario voters go to the polls Thursday.
— with files from Maria Babbage