Doug Ford just blew up the city of Toronto's election plans, and in the process he's setting up what could be some fierce fights between longtime councillors.

The premier shocked the city Friday by announcing he's killing the plan to expand the city's ward map to 47 wards — something a majority of councillors voted for in 2016 — and will use the 25-seat provincial and federal riding system instead.

The sudden reversal comes less than 100 days before the Oct. 22 election and will make a huge difference for both new candidates and incumbents. Here's a look at how several races will change.

Downtown showdown

Toronto's booming downtown core was set to get several new wards, an exciting development that was attracting a mix of young and diverse candidates and older, established politicians.

Now, incumbents — who always hold a massive advantage in municipal elections — will be the heavy favourites to win wards like Trinity-Spadina, Toronto Centre and Davenport, unless they decide to run against one another.

For example, here's a potential match-up in University-Rosedale: Joe Cressy versus Mike Layton versus Kristyn Wong-Tam.

Those three sitting councillors, who vote together on most matters, could divvy up downtown wards, but they'll still face stiff competition from the likes of former mayoral candidate George Smitherman, media personality Jennifer Hollett, and former TDSB trustees like Chris Moise and Ausma Malik.

A win for Scarborough

A quick look at the electoral map shows Scarborough, which has six wards (that's now more than the downtown core) may benefit the most from Ford's move.

Sitting councillors will likely shift around, but match-ups could include Coun. Michael Thompson taking on Coun. Glenn de Baeremaeker and Coun. Jim Karygiannis facing off against Coun. Norm Kelly.

How does Karygiannis feel? "Hell yeah, bring it on," he said of the redrawn boundaries on Thursday night.

Dozens of people from diverse backgrounds are also running to represent this part of the city, but now it will be an uphill battle.

Etobicoke showdown

The fiercest fights may come in Ford's home base of Etobicoke, where a number of conservative councillors will compete in three wards.

In Etobicoke North, Coun. Michael Ford, the premier's nephew, could take on Coun. Vince Crisanti, a loyal Ford supporter.

In Etobicoke Centre, Coun. Stephen Holyday and Coun. John Campbell will likely square off.

Wild Willowdale

Willowdale is one of Toronto's fastest growing neighbourhoods, as well as the site of a proposed redesign of Yonge Street that polarized council.

Coun. John Filion, who represented the area for decades, retired earlier this year, clearing the way for an open race, while the redrawn boundaries would have created two new seats instead of one.

There were 17 candidates vying for those two positions, but they'll now have to beat each other and incumbent Coun. David Shiner.

The only open seat

There's still one free ward.

Beaches-East York was left vacant after the departure of Coun. Mary Margaret-McMahon, who reached the term limit she set for herself. Around 20 candidates are expected to compete for the seat.

However, there is a possibility that a Danforth councillor — either Coun. Mary Fragedakis or Coun. Paula Fletcher — could shift to the area to avoid what could be a tough incumbent-on-incumbent battle.