Going into Decision Day, the race for the Western Conference's No. 1 seed is a dead-heat, setting up for a fascinating regular-season finale for the three clubs still in contention.

Ahead of their respective matchups, the Seattle Sounders, Sporting Kansas City and the Colorado Rapids could all still claim the top spot on the table, with Concacaf Champions League spots on the line (the top two finishers will clinch one) in addition to Audi MLS Cup Playoff seeding implications. All three clubs have already clinched a top-four seed and home-field advantage in Round One, with the Portland Timbers the other club already solidified in that group.

Here's what all three need to do to make their top-seed dreams a reality. Make sure to also check out Andrew Wiebe's Cheat Sheet for a full breakdown of what's at stake in every Decision Day match.

Currently holding a one-point edge on Sporting KC atop the table at 59 points from 33 matches, the objective for Seattle on Sunday is simple: Beat Vancouver Whitecaps FC at BC Place (6 pm ET | MLS LIVE on ESPN+) and clinch both the No. 1 seed and a CCL berth in one fell swoop.

The last time the sides faced off at Lumen Field on Oct. 9, Seattle took a dominant 4-1 victory, but it figures to be tougher sledding on Sunday against a Whitecaps team playing increasingly good soccer under interim head coach Vanni Sartini, and that needs a result on its home field to solidify its own playoff positioning. A draw in Vancouver could still see Seattle clinch the No. 1 seed if Sporting and Colorado both drop points in their matches, but that's not something the Sounders are going to want to leave up to chance.

All of that sets up for what should be a high-octane Cascadia derby.

"I keep trying to tell you guys, I say this until I'm blue in the face, MLS is a hard league," Sounders head coach Brian Schmetzer said at training this week. "If I'm looking at Sporting Kansas City and looking at it inward amongst ourselves, both teams have had chances to put this to bed already and we haven't done it. I appreciated what Peter [Vermes] said at halftime [against Austin FC on Wednesday], his team didn't perform. Sometimes that happens, it's pro sports. So, now it comes down to Decision Day, and we've got to make sure our teams perform."

If the Sounders win, Sporting KC can't finish any higher than No. 2 on the table, but that's still plenty significant given the CCL berth at stake. That makes Sporting's Decision Day matchup with Real Salt Lake at Children's Mercy Park (6 pm ET | MLS LIVE on ESPN+) a big one in its own right, as they'll look to ensure they don't fall down to the No. 3 spot.

With a win, they'll be in the top two, regardless of how the other results shape out. On top of that, Sporting know that if they win and Seattle drop points, the No. 1 seed is theirs regardless of what Colorado does, as they'd hold the first tiebreaker (total wins) on the Rapids.

If Sporting draw and Seattle and Colorado both lose, things become interesting. That would leave SKC and Seattle tied on 59 points and with 17 total wins, with the second tiebreaker being goal differential (Seattle are currently +20, Sporting are at +19). All eyes on the scoreboard.

They'll be dealing with a desperate opponent in RSL, which is just under the playoff line by two points beneath the LA Galaxy, but can vault back above it and clinch their spot with a win. Sporting KC will have the home-field advantage at Children's Mercy Park, where they're 9-2-5 on the season.

"This team has performed from my perspective exceptional over the course of the season," Vermes said on Saturday. "They've put us in a place where at the end of the season we're still fighting for first place in our conference, which, don't forget, we did it in '18 and we did it in '20. That's a compliment to those guys and they should be proud of that, they've made the playoffs again, we have home-field advantage at least in the first round, so we'll what happens on Sunday."

Colorado being in the mix for the top spot heading into the season's final day is really quite remarkable, given the degree to which they flew under the radar during preseason. No one had them in this position, yet here they are, with a realistic chance at vaulting atop the table after Decision Day, when they'll play host to LAFC at Dick's Sporting Goods Park (6 pm ET | MLS LIVE on ESPN+).

They'll need some help. Seattle and Sporting would both have to lose or draw in combination with a victory over LAFC to make it happen, but that's not an unthinkable proposition. Once again, there's also the CCL factor, as the No. 2 seed is still very much in play, even if they don't end up snagging the top spot.

"For us, we really need to focus on the task at hand," head coach Robin Fraser said. "As I said, [LAFC are] a very good team and very difficult to beat. Our focus is winning that game. We can’t control what Seattle or Kansas City [do]. There’s nothing that we can do that can affect that. The only thing we can do is control our own effort and intensity and concentration. We would like to feel like ultimately we can affect our game and that’s really all we can spend time thinking about.”