Ospreys head coach Sean Holley believes Saturday's Magners League clash with the Blues at the Liberty Stadium could be the region's biggest ever derby.
Both teams are fighting for one of the four Magners League play-off places.
The Ospreys are in fourth with the Blues and the Scarlets five points behind in fifth and sixth respectively.
"In the context of the season, as it is now, then possibly it is [the biggest Welsh derby in the history of the Magners League]," conceded Holley.
"We have had some big, big derby games when the LV= Cup was the EDF we played the Blues in the semi-final in the Millennium Stadium that was a massive, big occasion.
"Clearly the Scarlets derby for us is a massive game for us every Christmas, but in the context of this season it's a pretty big one, it's up there.
"There is a lot at stake in this one now. Clearly the Magners play-offs is the thing that is at the front of everybody's mind."
And history is on the Ospreys' side - the last three encounters between the two teams in the Magners League have all been won by the home side, while the Blues' only previous victory on Ospreys soil was 28-9 at Liberty Stadium on 22 December 2005.
But despite that advantage Holley takes nothing for granted.
"There is always so much at stake with these games," he said.
"There is international selection in a World Cup year, then it's seen as a trial match, and bragging rights is always a big one.
"More importantly, it's probably seen as a must-win game for both teams. With the Blues losing at home last week [to Munster] it's probably a game they feel they have to win.
"Likewise, we [lost] up in Edinburgh [last Saturday] and we want to put that right straight away, so [it's a] massive game. I just hope there is going to be a good turn out for it and it's a great occasion."
But as well as the Magners League play-off battle Holley believes the regions have a responsibility to give Welsh rugby a boost ahead of the 2011 World Cup following recent setbacks.
None of the four Welsh regions made the Heineken quarter-finals and Wales ended an indifferent Six Nations campaign with a fourth-place finish for the third consecutive season.
"There's a little bit of an air of a gloom with the Six Nations going well at one point [and then falling away], [and] all of us [the regions] not being in the Heineken Cup quarter-finals," added Holley.
"We [Wales] are ranked ninth in the world and there is all this sort of question marks over [Welsh rugby].
"It's up to us to up our game and produce performances and get in the top four and give our national team something, a bit of a fillip if you like, to go into the World Cup pre-season and push the national team on to some sort of success in the World Cup.
"That's got to be the aim I think."