SEATTLE -- Seattle's 3-1 win over Toronto FC to claim MLS Cup 2019, in front of a sellout crowd of nearly 70,000 fans on Sunday, was the culmination of a love affair between the city and the Sounders a decade in the making.

It's easy to forget, in the wake of the successful expansion launches of Portland, LAFC and particularly Atlanta -- which won MLS Cup in front of a similar sellout crowd last year and has surpassed the Sounders as the attendance leader -- just how unbelievable Seattle's support once seemed. When the Sounders played their first Major League Soccer game 10 years ago, no team in league history had averaged 30,000 fans per match. The Sounders broke the MLS record in their inaugural season, and again in each of the next four before eventually peaking at more than 44,000 fans per game in 2015.

None of that was predictable in 2009. At the time, the big question in Seattle sports circles was whether the excitement over the Sounders' debut could last. After all, it's common for expansion franchises to see their attendance decline in Year 2. The WNBA's Seattle Storm, for example, saw their average decrease by almost a third during their second season. And though the Storm have carved out an important place in Seattle's sports scene, winning three championships of their own, they've still yet to reach that inaugural attendance again.

Several factors helped the Sounders not only maintain, but actually improve their fan support in Year 2 and beyond.

First, the timing of the team's debut on the MLS stage couldn't possibly have been better. Without question, 2008 was the most miserable year in Seattle sports history. The University of Washington fielded the only winless FBS team. MLB's Mariners lost 100 games for the first time in 25 years. The NFL Seahawks, just three years removed from reaching the Super Bowl, bottomed out at 4-12. And, most painfully, the NBA SuperSonics moved to Oklahoma City after 41 years in Seattle.

Though the Sounders could never replace the history lost with the Sonics' move, their arrival helped fill a void in the Seattle sports landscape and the Sounders took full advantage by nailing the expansion process. Even their one misstep -- the team originally excluded Sounders, part of Seattle's soccer heritage dating back to their NASL participation from 1974 to 1983, from a fan naming vote -- only ended up increasing excitement when they reversed course.

Second, the atmosphere created by Sounders supporters made CenturyLink Field an experience unlike almost any in American professional sports at that point, with the Emerald City Supporters in the south stands leading chants for the full 90 minutes. That made Sounders matches more entertaining for casual fans and the home stadium a fortress for the team, rather than depressingly cavernous like other NFL stadiums used by MLS teams.

Thanks in part to their home crowd, the Sounders won -- and kept winning. From Day 1, they've consistently been one of the best teams in MLS. They've reached the playoffs in all 11 of their seasons, a new league record. And while it wasn't until Brian Schmetzer's promotion to head coach in 2016 that the Sounders were able to break through in the postseason and reach MLS Cup, they claimed the US Open Cup three consecutive years starting in their inaugural MLS season and added a fourth in 2014.

Still, none of that -- not even the MLS Cup the Sounders did win on the road in Toronto in 2016 -- could compare to the enthusiasm hosting MLS Cup generated in Seattle.

- Replay MLS Cup: Seattle Sounders 3, Toronto FC 1 (U.S. only)

"This week was a week I will not forget," majority owner Adrian Hanauer, who led the group that brought the Sounders to MLS, said in the winning locker room. "Starting 10 days ago with Toronto knocking off Atlanta and realizing, 'Holy crap, we're going to host an MLS Cup,' I made a concerted effort to appreciate it and breathe it all in a little bit, because that's not really in my nature."

The first two Sounders wins en route to the MLS Cup, over FC Dallas and Real Salt Lake, were modestly attended by Seattle standards with 37,000-plus fans. The combination of the Sounders' improbable upset over Supporters' Shield winner LAFC in the Western Conference finals and the opportunity to win a league championship at home -- something only the Storm, among the city's major pro sports teams, have done -- put them in the front of Seattle sports fans' consciousness and made the Sounders a hot ticket. When MLS Cup tickets went on sale nine days ahead of the match, the building sold out within 20 minutes, guaranteeing both the largest attendance ever for a sporting event at CenturyLink Field as well as the largest to watch soccer in the state of Washington. On resale sites, tickets were running more than $200 just to get in the door.

For Sounders forward and Seattle-area native Jordan Morris, the chance to play for a trophy in his hometown was a unique experience.

"I got emotional before the game because I was thinking about that," said Morris, whose father is the team's chief medical officer. "I was here at the first game 10 years ago, and now I'm on the field playing for a championship. It's pretty special."

Hanauer had a similar feeling a few hours earlier, when he reached Pioneer Square and saw fans already gathering hours before the match. More than anyone, he knows the hard work, planning and luck it took to get to this point.

"You're never quite sure how it's all going to shake out, but obviously you want to play for championships, you want to win championships," Hanauer said. "Doing it in your home city, where you were born and raised, it's pretty special to see the joy that you give fans and how beloved these players and coaches are. It's pretty cool.

"Sports moves communities and brings people together. To see what this group of players and coaches was able to do for this community, for those 69,000, for the hundreds of thousands watching on TV and giant watch parties, it's awesome. It's great for the city."