History has set an impressive stage for Sounders FC.

Since 2002, MLS teams have played 13 home-and-home series against Mexican opposition in CONCACAF tournaments — and won just once.

That lone triumph came 10 years ago, when the Kansas City Wizards beat Santos Laguna in the '02 Champions Cup quarterfinals. Mexican teams have followed that up in dominant fashion, earning 10 consecutive series victories against MLS by a combined 48-22 score.

Seattle hopes to reverse that lopsided trend at 5 p.m. Wednesday in the second leg of a Champions League quarterfinal at, coincidentally, Santos Laguna of Comarca Lagunera. The Sounders earned a 2-1 series advantage in the first leg last week at CenturyLink Field and need a win, tie or one-goal loss with at least two goals scored to advance.

Beating Santos, a co-leader in the Mexican Primera Division, would be a crowning achievement not only for Seattle, but for all of MLS. Only one league team has made the Champions League semifinals since 2008.

And the Sounders don't need reminding.

"We know the competition we're in, we know the stage that we're in and we know the importance of the game," said coach Sigi Schmid.

Before the series, technical director Chris Henderson said CCL success would "be great exposure for the club and a great statement of all the work that we've put in since the beginning of the franchise."

Earning a lead in the first leg has already put Seattle in rare territory.

In the previous 13 series between MLS and Mexican teams, only once had the MLS team won the opener. In 2007, the Houston Dynamo beat Pachuca 2-0 in the first leg, but then lost 5-2 after overtime in the second leg.

The Sounders, who have played eight games against Mexican teams in the past three years, will be ready for Santos' best shot in the series finale.

"No team is going to come in and surprise us," said midfielder Brad Evans. "We know what we're getting into with every game now since we've played good sides and tested ourselves."

And Seattle more than proved itself a good side last week.

Schmid was extremely impressed with his team's cohesion, fitness and mental toughness in the 2-1 first-leg victory at home, especially because it was the first competitive game of the year against a top-tier Mexican team in midseason form. The confidence gained might have been more important than the result.

"Our guys know how to play against them and know that they can play with them," Schmid said. "Certainly I think we earned some of their respect, as well."

If there's one last thing the Sounders might benefit from, it's the schedule.

MLS granted Seattle a Week 1 bye from league games last weekend to focus on the CCL, meaning the Sounders should be sufficiently rested before the crucial second leg Wednesday. Santos, however, had a Mexican Primera Division game Saturday — a 3-1 victory against Puebla — and chose to play nearly all of its starters.

Could fatigue set in?

"Those guys have played a lot — hopefully that will help us," Schmid said. "But when you're in the middle of the season and you're playing important games, somehow the mental fitness takes over, as well. I'm sure they're going to be ready."

Sounders add two

In two moves that all but finalized Sounders FC's opening-day roster, Seattle announced the acquisitions of midfielders Andy Rose and Alex Caskey on Tuesday.

Rose, 22, was signed after having been acquired in a draft-day trade with Real Salt Lake in January.

Caskey, 23, was added on a transfer from the Charleston Battery of the United Soccer Leagues. He was drafted by the Sounders in the third round of the 2011 MLS SuperDraft. While he didn't make the team last year, Seattle retained his MLS rights.

Thirty players now are on Sounders FC's active roster, the maximum amount allowed by the league. Defender/midfielder Amadou Sanyang does not count toward that total and will be transferred to Charleston, a move that's expected to be finalized in the next few days.

Joshua Mayers: 206-464-3184 or jmayers@seattletimes.com. On Twitter @joshuamayers.