Eddie Johnson, Landon Donovan and Mix Diskerud added second-half goals for the Americans, who will next play in Dallas on Wednesday against Honduras, which beat Costa Rica 1-0 Sunday night as part of a doubleheader before a sellout crowd at the home stadium of the Baltimore Ravens.
Assists aren't an official statistic in the Gold Cup, but Donovan set up three scores in a dazzling performance.
"I think Landon proved again today how valuable he is and now he can make a difference," coach Jurgen Klinsmann said. "This game was important for coaches to see who is a difference maker. Overall, we see our team clicking more and playing better and better."
To say the least.
The U.S. has won nine straight full internationals a record for the country's national team. The Americans have also prevailed in seven of their last eight Gold Cup matches, the exception being a 4-2 loss to Mexico in 2011 final.
"We are trying to catch up with the big teams in the world," Klinsmann said. "It's all about speed. I'm not talking about physical speed. I'm talking about mental speed, passing speed with every player going both ways. That's what we're working to. This is a process and I think that process is coming along."
Rodolfo Zelaya scored for El Salvador, 1-19-7 overall against the U.S.
"Collectively, they're a very good team," El Salvador coach Agustin Castillo said through a translator. "They almost play by memory. They can find the spaces. It almost seems like every time they pass the ball into a space it's going to nobody, then somebody appears and actually meets the ball. Good work, good movement."
And good enough to claim a fifth Gold Cup.
"They're going through a very good time," Castillo said. "They're the best team I've seen in this tournament. They are a candidate to win it all."
In the other quarterfinal Sunday, Andy Najar interrupted a defensive struggle with a goal in the 49th minute, and Honduras squeezed past Costa Rica. After Najar scored on a header off a fine crossing pass from Alexander Lopez, Honduras goalkeeper Donis Escober made the advantage stand up.
Storylines U.S. 5, El Salvador 1
R Clarence Goodson and Joe Corona score in the first half for the U.S.
• Landon Donovan scores a goal and sets up teammates for three others.
• The U.S. advances to face Honduras in a semifinal Wednesday.