Defense wins championships, and that saying held true for the United States as the back line fueled a 2-0 victory over El Salvador on Wednesday. The American success against a relentless El Salvador attack will return the team to the semifinals of the Gold Cup.

With the victory, the team advances to the semifinals to face Costa Rica, which defeated Panama, 1-0, earlier in the night. This stage of the Gold Cup is familiar territory for the U.S., which will look to avenge a stunning semifinal loss in the 2015 Gold Cup in Saturday's game. But the Americans will have to find a better offensive rhythm after struggling to set a tone in a stilted match against El Salvador.

"I don't think games should look like that," head coach Bruce Arena said. "I thought we had a difficult time tonight. The game had no rhythm with all the fouls and players falling on the ground, but we weren't good on top of it. It took us 30 minutes to play a little bit."

The first half started out at a breakneck pace, fueled by a crowd split evenly for El Salvador and America at Lincoln Financial Field. Both teams set an aggressive tone, and the referees were forced to hand out yellow cards throughout the night as bodies hit the ground. The physicality intensified over 90 minutes, with play jerking to a halt every handful of minutes for a foul.

The moment of the match came on a dead ball in the second half, when Henry Romero reached around Jozy Altidore and grabbed the forward's nipple as the two bodied up before a corner kick. The forward dropped to a knee, then whirled and knocked Romero to the ground.

"My girl is mad at me," Altidore joked after the game. "She's mad at me, she's mad at Romero. She's like 'Only I can bite you, only I can grab your nipples.'"

Despite the fouls, the U.S. wasn't lacking opportunities from its offensive leaders. The team leveled 14 shots, with eight coming on frame, and dominated possession for 59 percent of the game. Altidore, Arriola and Dempsey found space to attack the net. But both of the first-half goals started with feeds from one of the Americans' most seasoned stars, and ended with textbook finishes from a defender.

After a shaky start, the U.S. attack found its rhythm in the gut of the first half. Gyasi Zardes slipped off the line to slam a shot into the net in the 30th minute, but the goal was called back with an offsides call from the referee.

Ten minutes later, Zardes took a hard foul on the left side of the field and set up the team's first goal. Michael Bradley, the American captain who joined the team after group play, took the free kick, bending the ball towards the mouth of the goal. The pass looked too high, but defender Omar Gonzalez — who towers over most opponents at 6-foot-5 — leapt skywards and flicked a header just over the fingertips of goalkeeper Derby Carillo.

Behind the goal, the fans in the American Outlaws' section roared to their feet. Gonzalez isn't much of a shooter, but all three of his career goals have come from in a Gold Cup. With the scoreboard reading, 1-0, the momentum of the game swung towards the Americans in the waning minutes of the half.

Clint Dempsey set up the brace for the U.S., turning deftly at the top of the box in the 46th minute and slicing a pass to the feet of Eric Lichaj, who was streaking toward the goal. Lichaj took one touch and fired. The shot flew between the goalkeeper's legs, and Lichaj sprinted to the corner, throwing himself into a slide. He flopped on his stomach, laying still for a moment before his team mobbed him.

At the bottom of the dogpile, Lichaj smiled out of relief, exhausted. His first touch of the game was a sloppy back pass that was intercepted by a Salvadoran forward and almost converted into a goal. Howard flew off his line, diving to kick the ball away. For Lichaj, the goal came as a comfort after early mistakes.

"The first 45 [minutes] were really bad," Lichaj said. "My first pass back to Tim [Howard] was very bad. I told him thank you after the game because … he got me out of the dirt. I needed that goal, if anything, because I wasn't having the best of games."

Lichaj's goal was the knockout punch the Americans needed to win the match. El Salvador made it clear that they weren't going down quietly, but the team also struggled to capitalize on scoring opportunities in both halves. The Salvadorans thrived on counterattacks, driving at the backline to force mismatches. But even on one-on-one match-ups with goalkeeper Tim Howard, the team failed to place a shot on goal, with wide open opportunities flying high and wide.

As they have in every game of the Gold Cup thus far, the Americans breathed a sigh of relief as the final whistle blew.