The defending champion Seattle Sounders are returning to the Western Conference finals for the fourth time in the last six years, a feat currently unmatched in Major League Soccer. But it has not been the easiest title defense, not by any stretch.

“It has been a challenging season, to say the least,” said Sounders head coach Brian Schmetzer after the Sounders knocked the Vancouver Whitecaps out of the Western Conference semifinals on Thursday night.

The Sounders hoisted the MLS Cup in Toronto last December, the first league title in the club’s eight-year history. Before the season they were a trendy pick to repeat. That historic run from the dregs of the Western Conference in late July, after all, was largely accomplished without Clint Dempsey, sidelined from late August onward with an irregular heartbeat. Pair Dempsey’s return with the first full season in MLS for Uruguayan playmaker Nicolas Lodeiro — not to mention a year of growth for young U.S. international Jordan Morris — and it’s easy to see why the word “juggernaut” was bandied about in season previews.

Not so much, it turned out.

The Sounders limped out of the gate in more ways than one. Injuries ravaged the back line for nearly half the season. Schmetzer trotted out his first-choice defense for the first time in Week 15, and still couldn’t field a consistent group until right fullback Kelvin Leerdam arrived from the Netherlands in the summer transfer window.

And it has to be acknowledged: A team that electrified crowds down the stretch last season simply looked sluggish for long stretches of spring and early summer.

“I think we started off this year with a little bit of a hangover,” Schmetzer said Thursday. “I thought there were some guys that maybe were still celebrating our championship.”

To make matters worse, Dempsey and Lodeiro, so tantalizing when briefly glimpsed together in 2016, struggled to mesh and always wanted to occupy the same place and do the same things.

And while Morris continued to stretch defenses with his speed and hustle, he struggled to find the back of the net. After scoring 12 goals in a sterling rookie campaign, the Seattle-area native netted just three times in 23 appearances this season and repeatedly failed to put routine shots on frame. He has been sidelined with a strained hamstring since early September.

But just as they did last year, the Sounders turned things around in the second half of the season. Seattle began the campaign with just two wins in its first 11 matches (2-5-4) but closed it with just two losses in its last 18 (9-2-7). They are undefeated in their last four home games, winning by a combined score of 12-0.

Defense, opportunistic play, and a certain grimy determination and championship poise fueled the turnaround.

“This team has figured out a way to win games again,” Schmetzer said.

Counting their two playoff matches, the Sounders have delivered shutouts in 11 of their last 16 games. They have given up multiple goals only twice since July 19. Rugged central defenders Chad Marshall and Roman Torres have been excellent. Leerdam has been solid in defense and dangerous in attack. Goalkeeper Stefan Frei has maintained a 1.09 goals-against average while delivering the occasional jaw-dropping save. Whoever Schmetzer inserts in front of the defense — Osvaldo Alonso, Cristian Roldan, Gustav Svensson, Jordy Delem, even Lodeiro on Thursday thanks to injuries — has done yeoman’s work protecting the top of the penalty area.

Perhaps nothing exemplifies this Sounders run better than the two-legged victory over the Whitecaps in the conference semifinals. A team once known for looking overwhelmed by road playoff games (back-to-back 3-0 road losses in 2011 and 2012 are perhaps the low points in the club’s MLS history) traveled to Vancouver and ground out a perfectly boring and utterly professional scoreless draw in the first leg.

In the return leg at CenturyLink Field, the Sounders found themselves stymied for nearly an hour by a Vancouver side that sometimes packed seven defenders in the box. Yet Seattle maintained its poise and actually grew more patient over the course of the match, increasingly switching the point of attack and waiting to pounce on Vancouver’s first mistake.

That mistake came in the 56th minute, courtesy of a midfield turnover by none other than former Sounder Fredy Montero. Some beautiful combination play then left Dempsey open at the top of the penalty area, and he proceeded to create space for a left-footed laser that gave the Sounders a 1-0 lead. He would add a late insurance goal with a volley at the doorstep in the 88th minute.

“There were times in the game,” said Dempsey after the match, “where we were losing the ball too easily and, you know, letting them have more of the possession. But once we got more control of it and kept better possession in the attacking third, we were able to get better looks in front of goal. We just kept getting better and better looks. There could have been a few more [goals].”

While neither game was especially beautiful, they were also results the Sounders might not have secured in years past.

“I think the run from last year certainly helps,” said Schmetzer. “There are guys on that roster that played last year. But I would expand that to say the team is a pretty veteran team.”

The Sounders now advance to play either the Portland Timbers or Houston Dynamo. That series is tied 0-0 heading into the second leg at Portland’s Providence Park. The Sounders will also have almost three weeks to get healthy. Morris (hamstring), Svensson (hamstring), Alonso (quad), and Victor Rodriguez (quad) were all either absent or limited against Vancouver with leg injuries.

And with Dempsey looking dangerous and a talented roster that won MLS Cup just a year ago, Schmetzer likes the Sounders’ chances in the conference finals and beyond.

“If we get past Houston or Portland,” said Schmetzer, “We’d have a good shot at anybody to repeat as champions.”