The four-time All-Star spent 10 seasons with the Sounders, captaining the team to its first MLS Cup in 2016, and seemed destined to finish his career there. But prior to the 2019 season, the two sides failed to reach agreement on a new contract and Alonso left via free agency, signing with Minnesota.
The former Cuba international, who became a U.S. citizen in 2012, was one of the main players brought in by manager Adrian Heath to get the Loons among the upper echelons of the league. Monday's Western Conference final means the fourth-year franchise is just one win away from a first MLS Cup final appearance.
It is the Sounders who stand in its way, and after facing Seattle twice last year, Alonso no longer feels any discomfort at playing his old team, though he has fond memories of a decade spent in the Emerald City.
"I've got Seattle in my heart," he told ESPN. "They gave me the opportunity to play in MLS when they came into the league. I've got my two daughters who were born in Seattle, so for me, Seattle is like a home."
Minnesota has been good to Alonso as well. The team has experienced steady improvement since his arrival, qualifying for the postseason last year before a deeper run this campaign. And while Alonso was limited to 10 regular-season appearances, he has been there when it counted, including a starting role in the Loons' dominant 3-0 Western Conference semifinal win over Sporting Kansas City.
"It's about leadership," Heath said of the 35-year-old's influence. "And people talk about that like it's always a throwaway comment. But every day he trains properly and brings positive energy within the locker room."
Heath recalls the first day that Alonso arrived ahead of the 2019 campaign. The Loons had been a laughingstock their first two seasons in the league, conceding a total of 141 goals. Alonso made it clear that wasn't going to happen again.
"We had a little chat about the season and how it was going to go," Heath said. "And he said, 'I've made the playoffs 10 years in a row, and I am not f---ing letting that go, so let's get it in our head here that we're going to make the playoffs, and that's the minimum of what's expected of us.'"
That attitude has seeped into the team's younger players, including the man widely picked to take over for Alonso in the center of Minnesota's midfield. Hassani Dotson, a Seattle native, grew up attending Sounders matches and quickly gravitated toward Alonso and Fredy Montero as his favorite players.
"Fredy had all the flavor, but I thought Alonso was so consistent," Dotson said. "Sometimes his great performances would go unnoticed, but I was always a big fan of his."
That support did not waver, even as he got cut from the Sounders' pre-academy team when he was 14 -- "I was only a fan of the first team" -- and his admiration for Alonso continues, albeit in a different way.
"You can see he's a big competitor like I am, but he just does all the right things in terms of taking care of his body, paying attention to detail and trying to win every single aspect," Dotson said. "And I think that's pretty cool, to see someone that's played and won many things to still have that drive to keep winning. So I think that is pretty contagious on the rest of the team."
Granted, Alonso isn't the only player having an influence on the Loons' success. Defender Michael Boxall has filled in capably for Ike Opara, who has missed most of the year through injury. The four-headed hydra of Ethan Finlay, Robin Lod, Kevin Molino and Emanuel Reynoso has been devastating in attack, especially in the postseason.
Credit must also be given to Heath, who seems to be making all the right moves.
"Adrian was a player; he's intense. He likes to win," Alonso said. "He's got that inside of him, to push us to do more. I think it shows every time we play. I think our team is like him. Do more, do more. I think we are in the conference final because of him."
And yet come Monday, plenty of eyes will be on Alonso -- both from friend and foe -- to see if he can summon up another impactful performance on Seattle turf. Ever the competitor, he is confident that he can and, moreover, thinks he has a couple of years left in him.
"When I'm healthy, I feel good, I can run," he said. "I go year by year, trying to do my best, hoping they will give me the trophy."
In 2020, Alonso must go through Seattle to get it.