TUKWILA — The U.S. Open Cup story doesn't change much for Sounders FC — not like the team thinks anything is wrong with that.

It's a winning tale.

Midfielder Osvaldo Alonso had a goal and assist, and four different Sounders scored as Seattle pulled away late from Chivas USA in a 4-1 semifinal win Wednesday in front of 4,500 at a sold-out Starfire Stadium.

The three-time defending champion Sounders will go on the road to face Sporting Kansas City in the final on Aug. 8. Seattle could become the first team in the tournament's 99 years to win four Open Cups in a row; three other teams have won three straight.

So how much will the Sounders play up the opportunity at writing history?

"We'll be very aware when we step on the field in Kansas City that we have a chance to do something nobody has done," said coach Sigi Schmid.

Added midfielder Brad Evans: "Just the chance isn't good enough for us. ... We want this one, so let's make history."

Nursing a 1-0 lead at halftime Wednesday, the Sounders earned some comfort room in the 48th minute when Alonso craftily chipped in a penalty kick, his fourth goal of the tournament, to double the advantage. Forward Fredy Montero drew the PK a minute earlier when he was dragged down in the penalty box by Chivas defender Rauwshan McKenzie.

History suggested Seattle's lead would be safe — the Sounders have never allowed more than one goal in an Open Cup game — but things got interesting.

Chivas USA pulled a goal back in the 74th minute when forward Cesar Romero, a second-half substitute, put away a rebound of his own miss.

Seattle sealed the win in the 83rd minute, however, when Evans was found wide open on the right by Montero and calmly finished the scoring chance. Sounders forward Sammy Ochoa put an exclamation point on the night with a goal in the 88th minute.

In the final moments of the game, the crowd burst into a loud chant of "We're going to win the U.S. Open Cup!"

Veteran forward Eddie Johnson, who scored Seattle's first goal in the 31st minute off an Alonso assist, said next month's final would be "one of the biggest games of my career."

The Sounders improved to 9-0 in the Open Cup when leading at halftime and 15-0-1 when scoring first. But all records will look good when you haven't lost a tournament game in four years.

The only regret from the night was that the final won't be played back at CenturyLink Field.

Seattle won its first Open Cup in 2009 on the road against D.C. United, then successfully defended the title the next two years at home against Columbus and Chicago, respectively.

"It would've been great to play at home, because I think we would've had more than we had last year," said Schmid in reference to a crowd of 35,615 in 2011. "I think to set the record of four in a row, who knows, maybe we would've sold out the whole place at 60,000. But we're going to Kansas City. It means the first one we won on the road, and we're going to try and win the fourth one on the road."

Notes

• Seattle beat Chivas USA, 3-1, in an Open Cup semifinal in 2010.

• Sporting Kansas City advanced with a 2-0 road victory over the Philadelphia Union. Jacob Peterson and Graham Zusi had the goals for Sporting KC.

• Two former Sounders were available for the visitors: defender James Riley, who started, and midfielder Peter Vagenas, who was on the bench.

• Seattle improved to 12-0 in Open Cup games at Starfire.

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

SOUNDERS 4, CHIVAS USA 1

Shots — CHV 4, SEA 18. Shots on Goal — CHV 4, SEA 9. Saves — CHV 5, SEA 3. Fouls — CHV 15, SEA 17. Corner Kicks — CHV 1, SEA 6. Offsides — CHV 2, SEA 5.

CHV Starters: Kennedy, Riley, Califf, McKenzie, Villafaña, Minda, Zemanski, Gavin, Moreno, Cardozo, Angel. Subs: Romero. SEA Starters: Meredith, Scott, Hurtado, Ianni, Gonzalez, Cato, Alonso, Rose, Caskey, Montero, Johnson. Subs: Evans, Fernandez, Ochoa. Att.-4,500