One of these two teams is on a three-game winning run in the Heineken Cup. With their injuries, few would have guessed it would be Cardiff.
After losing at Exeter, the Blues haven't looked back as wins over Toulon and Glasgow at the Arms Park were furthered by victory at Scotstoun.
They also claimed a much-needed PRO12 win against the Dragons last time out as their defence again stood out. It will need to again this week.
Toulon meanwhile enter this probably Pool deciding game in turmoil after a home defeat to Grenoble in the Top 14, a loss that led to head coach Bernard Laporte's future being up in the air. The big question now will be how his team responds at this clash at the Allianz Riviera.
Subsequently Cardiff definitely have a chance of continuing their spirited revival in the Heineken Cup on Saturday but must do so without attacking weapon, Rhys Patchell, who is ruled out for four months with a knee injury. Gareth Davies, the try hero from Round Two, replaces him.
Loosehead prop Gethin Jenkins will captain the visitors and makes his first start for the region since October as Blues face a crunch clash in Pool 2 against the French giants.
Director of Rugby Phil Davies makes a total of five changes to the side that beat the Dragons.
The other change in the pack is a recall for lock Chris Dicomidis, with Macauley Cook moving to the back-row.
Chris Czekaj is named on the wing as Harry Robinson misses the game with a leg injury.
The final change sees Gavin Evans named at inside centre where he will form a new-look midfield partnership with Richard Smith.
Davies said: "Toulon will be smarting from last week's defeat in the league and they won't have been happy they lost the game to us in Cardiff earlier in the season. It's a massive challenge and they will be extremely motivated. But it is one we are ready for.
"They have huge quality in the team they have got but we are going out there to try and win. We will do the best we possibly can and the attitude in the squad is terrific.
"Throughout the season we have got better without the ball and with it we have controlled it. We now need to finish more and get a few more tries. We have got to be aggressive with or without the ball to match what Toulon throw at us."
Meanwhile, Toulon have dropped Delon Armitage to the bench for their clash in Nice.
Drew Mitchell wears the full-back jersey while fellow Australian Matt Giteau returns at inside centre in place of Maxime Mermoz. He partners Mathieu Bastareaud in the midfield.
In the pack Joe van Niekerk and Craig Burden start at flank and hooker respectively.
Toulon: 15 Drew Mitchell, 14 Rudi Wulf, 13 Mathieu Bastareaud, 12 Matt Giteau, 11 David Smith, 10 Jonny Wilkinson (capt), 9 Sebastien Tillous-Borde, 8 Steffon Armitage, 7 Joe van Niekerk, 6 Juan Smith, 5 Jocelino Suta, 4 Bakkies Botha, 3 Carl Hayman, 2 Craig Burden, 1 Andrew Sheridan.
Replacements: 16 Jean-Charles Orioli, 17 Florian Fresia, 18 Martin Castrogiovanni, 19 Pierrick Gunther, 20 Delon Armitage, 21 Maxime Mermoz, 22 Frederic Michalak, 23 Konstantine Mikautadze.
Cardiff Blues: 15 Leigh Halfpenny, 14 Alex Cuthbert, 13 Richard Smith, 12 Gavin Evans, 11 Chris Czekaj, 10 Gareth Davies, 9 Lloyd Williams, 8 Robin Copeland, 7 Josh Navidi, 6 Macauley Cook, 5 Filo Paulo, 4 Chris Dicomidis, 3 Benoit Bourrust, 2 Marc Breeze, 1 Gethin Jenkins (capt).
Replacements: 16 Rhys Williams, 17 Sam Hobbs, 18 Scott Andrews, 19 James Down, 20 Ellis Jenkins, 21 Lewis Jones, 22 Dafydd Hewitt, 23 Dan Fish.
Date: Saturday, January 12
Kick-off: 16:40 local (15:40 GMT)
Venue: Allianz Riviera, Nice
Referee: Greg Garner (England)
Assistant referees: Steve Lee (England), Andrew Pearce (England)
Television match official: Rowan Kitt (England)