With the host team looking to win the tournament for a sixth time, centre back Gonzalez broke the deadlock when he deflected Michael Bradley's free kick into the net with a diving header in the 41st minute.
Right back Lichaj then ran onto Clint Dempsey's through ball to double the advantage in first-half stoppage time when he beat goalkeeper Derby Carrillo with a firm, low shot.
Midfielder Gyasi Zardes might have scored earlier for the U.S. but his lobbed effort was ruled out for a narrow offside decision.
However, while the U.S. defence may have made a telling contribution to the side's attack, mistakes at the back could have cost the hosts dearly.
El Salvador almost scored with their first attack when striker Rodolfo Zelaya pounced on a poor back pass by Lichaj but was brilliantly foiled as he entered the area by the out-rushing Tim Howard's dive to palm the ball away from his feet.
Early in the second half, Gonzalez's central defensive partner Matt Hedges was caught in possession near the centre circle by Zelaya, who attempted an audacious lob with Howard off his line, only for the ball to sail over the bar.
Soon after, Denis Pineda skimmed the outside of the post after taking advantage of a misunderstanding between Lichaj and Darlington Nagbe.
As the U.S. defended their unbeaten home record in 16 matches against El Salvador, the Central American team's defender Henry Romero appeared to bite striker Jozy Altidore's back in the box as they jostled for position at a corner.
In Thursday's quarter-finals in Glendale, Arizona, tournament favourites Mexico face Honduras and 2015 runners-up Jamaica meet Canada.
(Reporting by Rex Gowar; Editing by John O'Brien)
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