SALT LAKE CITY – Few give due credit to the goalkeeper after a 6-0 win.

Buried beneath the avalanche of late Sounders goals in Wednesday’s U.S. Open Cup rout of Chicago were Stefan Frei’s string of vital first-half saves.

In the 16th minute, the Seattle keeper sprawled to his right to keep out a low drive from Quincy Amarikwa.

Five minutes later, Frei blocked a free kick with his chest, then swatted the rebound aside with a big left paw.

If either shot finds the net, the early Sounders goal gets cancelled out, the score evens up and the whole match changes.

The margin for error will be even thinner Saturday afternoon when Seattle takes on Real Salt Lake at Rio Tinto Stadium in Utah in a match-up between the top two teams in the Western Conference.

Seattle has a two-point edge in the standings, there’s an unusual kickoff time of 11:30 a.m. PT and the weather is forecasted at 86 degrees at kickoff.

Frei’s opposite, Nick Rimando, is also the new all-time MLS shutout leader with 113.

“We know Rimando’s strengths,” Seattle attacker Lamar Neagle said.

“He’s a great keeper. We know we’re going to have to do something special to beat him.”

Frei is still working himself back into top shape after missing most of the 2012 season with a broken leg and spending the bulk of 2013 as a back-up in Toronto before being traded to Seattle last offseason.

“It’s been a process,” Sounders coach Sigi Schmid said.

“But I can tell the confidence is growing all the time. I’m very happy with how he came along.”

Saturday represents one of his biggest tests in a Sounders uniform: A parry here or a fingertip there could be decisive in a matchup of teams as even as these.

In 13 all-time league matchups, Salt Lake has won five and Seattle four, with the pair sharing four draws.

The Sounders have scored 14 goals and Real Salt Lake 11, the former padding the gap with a 4-0 victory in Seattle in late May.

“It’s going to be a battle,” Sounders midfielder Osvaldo Alonso said. “It always is with Salt Lake.”

The men between the posts won’t man the first line of engagement, or even the second.

But they represent the final one.

Matt Pentz: 206-464-3184 or mpentz@seattletimes.com. On Twitter @mattpentz.