Felix Auger-Aliassime and Denis Shapovalov stunned defending champions Russia Saturday in a decisive doubles rubber to send Canada storming into an ATP Cup final against Spain.

Their Sydney showdown went to the wire after Shapovalov neutralised Roman Safiullin 6-4, 5-7, 6-4 in the opening singles match.

But world number two Daniil Medvedev then thrashed 11th-ranked Auger-Aliassime 6-4, 6-0 to level it up with a flawless performance in an ominous warning ahead of the Australian Open later this month.

It forced the match into a doubles shoot-out which looked to be going Russia's way only for Canada to find an extra gear and grind out a 4-6, 7-5, 10-7 win to make their first-ever final in the team event.

"Felix did an amazing job. I had a little bit of a slow start, had trouble returning, but we did a good job to fight," said Shapovalov, who missed Canada's first singles match at the tournament while he recovered from Covid-19.

"We have great team chemistry, team spirit, so it helped us a lot."

Auger-Aliassime admitted he was down on confidence after crashing so heavily in the singles against Medvedev, but said his long-time friend Shapovalov helped him re-focus.

"I had to try and stay positive. Of course, it was tough, especially (because) that second set went the way it went in singles," he said. 

"Denis helped me and the team to push myself. We had a tough start in the doubles, so to be able to come back in this way, it's really a team effort.

"That's what the ATP Cup is about. You can still win after being 1-all and losing a tough singles."

Their reward is a clash with 2020 runners-up face Spain on Sunday and they have a big task ahead against the unflappable Roberto Bautista Agut and his solid teammate Pablo Carreno Busta.

Both players are both in red-hot form, each winning all four of their singles encounters so far.

Super tough 

Medvedev led Auger-Aliassime 2-0 in their singles head-to-heads going into Saturday's match, with his most recent triumph coming in a massive clash in last year's US Open semi-finals, a tournament he went on to win.

But Auger-Aliassime nevertheless had confidence heading into the match after defeating world number three Alexander Zverev on Thursday.

The Russian master, however, never let him settle and cruised to victory in 69 minutes.

The Canadian started well and used his serve to control points, but when he was broken at 4-4 in the first set his game unravelled.

"He was serving just aces, playing good, so I knew I just had to stay in the match, try to do what I can, what's possible against his big game," said Medvedev, who will be the top seed at the Australian Open should Novak Djokovic not play.

"He definitely started to play a little bit worse and I managed to use it, and that was the key today."

Shapovalov earlier had to work hard to put away the gritty Safiullin, with his serve and baseline game ultimately proving too much in the crucial moments.

"Definitely super tough. Obviously Roman is playing with a lot of confidence," said Shapovalov.

"He's a great player and surely he’s going to have an amazing season, so I'm very happy to get the win. It was definitely very tough."