Former Wales international Rhys Williams believes Cardiff Blues' trip to Newport Gwent Dragons in the first European Welsh derby for 15 years on Saturday is too close to call.
The two regions meet at Rodney Parade for a place in the European Challenge Cup semi-finals, as well as the honour of being the last Welsh side standing in continental competition.
The last meeting between two Welsh teams in Europe pre-dates regional rugby - Llanelli knocked Cardiff out at the same stage of the 1999-00 Heineken Cup - and Williams, who spent a decade at Cardiff Arms Park as a player, predicts another close battle following an away win apiece in the Pro12.
"It's good to see the Dragons and the Blues doing well in the competition," he told Perform. "Unfortunately they're going up against each other, but that will be a good Welsh clash.
"I'm sure that will be as competitive and as fiery as any game. I see it being a very close match.
"Going down to Rodney Parade, it's always a very dogged game and without a doubt it will be a very intimidating atmosphere.
"The supporters there are very close to the pitch and there's no love lost between the Gwent supporters and Cardiff.
"Those are the games that players really get up for and the reason why we all grow up wanting to play rugby. We want to play in these big derby games and cup matches and to test yourself against some of the better teams around.
"It's a slightly different dynamic when it's your next-door neighbour and a lot of the players will know each other and they'll be looking to settle scores and get one over on somebody they know.
"It'll be a tough game, a very tough game, and I don't want to call a winner."
The reward for the victors of that clash will be a trip to face the winner of the match between London Irish and Edinburgh, which takes place at the Madejski Stadium on Sunday.
Gloucester and Connacht kick off the weekend's action at Kingsholm on Friday, with the hosts - winners of both previous meetings between the sides - having failed to make it past the Challenge Cup quarter-finals in their last three attempts.
Exeter Chiefs or Newcastle Falcons await Gloucester or Connacht in the semi-finals.