In six league matches, Vancouver (7-5-5) have come close — extremely close on some occasions — to beating their bitter Pacific Northwest rivals, but they only have three draws and three losses to show for their efforts.
If Vancouver fails to win against the Sounders (7-5-3) in front of a sell-out crowd at BC Place on Saturday night, the trite questions posed to Rennie and his players by reporters about why they can't beat Seattle will continue to be asked.
But the coach isn't perturbed by this winless run against the Sounders, pointing out his team recorded first-ever wins over LA Galaxy and New York Red Bulls already this season.
"The fact that we've not beaten Seattle is not something that concerns me too much," he said Friday. "It's just another game and we need to make sure that we're at our absolute best.
"We're very determined to do well, especially at home, and we want to keep our run going and we want to of course beat Seattle. That's the big thing that people talk about."
Both the Whitecaps and Sounders head into the sell-out clash full of confidence, with Vancouver picking up five wins in its past eight games and Seattle collecting six victories in the same span.
However, Vancouver is one of only two teams who have not lost at home in MLS this season, and it's that dominance at BC Place — along with the team's form of late — that is pushing the players to break the drought.
"We kind of owe them," said Whitecaps midfielder Matt Watson. "We haven't won a Cascadia Cup game yet so we really need to get our account opened and it means a lot to fans and it means a lot to us.
"It's a season where you obviously play lots of different teams, but these games have that little bit extra.
"I think we're all conscious of that (having not beaten Seattle) in the back of our minds and we feel like this is the time, we're full of confidence, and if we're going to beat them, this is the time to do it."
Vancouver sits fifth in the Western Conference on 26 points, but Seattle is just two points back in seventh spot.
The Sounders also have two games in hand but according to Kenny Miller, it's something the team won't be using as an extra incentive to win.
"That's the way the league kind of works," he said. "We've got games in hand on teams above us as well.
"Obviously Seattle are behind us and will be looking to jump us if they win, so it's important that we make sure that doesn't happen. But if we can win, it puts an extra bit of daylight between them and us and cements us right in that playoffs spot."
Whitecaps defender Andy O'Brien has recovered from a hamstring injury, but Rennie was pleased with the performance of central defensive duo Brad Rusin and Johnny Leveron in the 1-1 draw at Sporting Kansas City midweek so there's a "fair chance" O'Brien will be rested.
South Korean full-back Young-Pyo Lee returns to the lineup after skipping the recent two game road trip, allowing Englishman Nigel Reo-Coker to return to his familiar spot in midfield.
Seattle will likely be without key central midfielder Osvaldo Alonso (quad) once again while fellow midfielder Steve Zakuani is also injured.
Team changes aside, both teams boast strikers who are in red-hot form, with Vancouver riding Camilo's 10 goals - which is joint second-best in the league - and three assists, while Seattle can return fire with former Inter Milan striker Obafemi Martins, who has six goals, including three game-winners.
Martins can also be used as a barometer for Seattle's performance this season. Whenever he has scored or assisted on a goal, the Sounders are 6-0-0.
Saturday's game against Seattle will be the third game in a week for Vancouver, but Watson - who ran himself ragged in last Saturday's win at DC United - says the significance of the match will force the players to dig deep.
"Obviously the energy levels aren't as high as they could be," he said. "But the game itself is a huge game and everyone's got to get up for it. There's going to be no excuses and we're going to be as ready as we can be."