First-half goals from defenders Omar Gonzalez and Eric Lichaj secured a hard-fought quarter-final win for the hosts.
First-half goals from defenders Omar Gonzalez and Eric Lichaj secured a hard-fought quarter-final win for the hosts, who are chasing their first Gold Cup title since 2013.
However Bruce Arena's side were made to work all the way by El Salvador, and only some superb saves from Tim Howard kept the Central American side at bay at Philadelphia's Lincoln Financial Field.
"They pressed us well and we weren't good enough with the ball to break their press," Howard said afterwards. "We got the two goals before half-time and that was obviously good for us. But we knew they were going to cause us problems.
"It's good to get the win. We can work on a few things, but that's what this tournament's about."
An unconvincing start saw the hosts given a let-off early on when Lichaj under-hit a back pass to Howard.
Rodolfo Zelaya latched onto the loose ball and darted clear only to be denied by a desperate late block from Howard, who had spotted the danger and advanced swiftly to snuff out the chance.
The remainder of the first half was dominated by a series of niggly fouls as El Salvador frustrated American efforts to impose themselves on the contest.
The Americans were unlucky to be denied an opening goal midway through the half when Clint Dempsey released Gyasi Zardes who lifted his finish above Derby Carrillo, only to be flagged for offside.
Replays later showed the Los Angeles Galaxy forward was onside.
As tempers flared Lichaj was lucky to escape a caution when he flattened Dennis Pineda near the halfway line.
Four minutes before halftime however, the US broke the deadlock when Gonzalez leaped to glance in Michael Bradley's teasing free-kick to make it 1-0.
Deep into first half stoppage time, Lichaj made it 2-0 with a goal that owed everything to the guile of Bradley.
The veteran striker left Henry Romero for dead with a brilliant turn and then slipped a pass into the feet of Lichaj, who controlled to shoot beneath Carrillo for his maiden international goal.
The Americans now face 2014 World Cup quarter-finalists Costa Rica in Saturday's semi-finals.
The match represents an opportunity for the US to avenge their humiliating 4-0 loss to Costa Rica during 2018 World Cup qualifiers last year.
Howard however insisted score-settling would not be on the agenda.
"It's not about what happened in the past," he said. "It's about winning on Saturday night and getting to a final."
Los Ticos advanced to the last four after Panama defender Anibal Godoy headed agonizingly into his own net to give Costa Rica a 1-0 victory in Wednesday's earlier quarter-final.
The Central American rivals were deadlocked in the second half when Costa Rica's David Guzman swung a long free kick toward the Panamanian goal.
Panama's Godoy leapt to try to head the ball away but instead it spun back into the Panamanian net in the 77th minute.