PHILADELPHIA — In any tournament knockout game, the most important thing is to survive and advance.

But members of the US national team know they won’t survive much longer in the Gold Cup if they play anything like they did in Wednesday’s 2-0 quarterfinal win over El Salvador at Lincoln Financial Field.

“I thought we had a difficult time tonight,” head coach Bruce Arena admitted after the match. “Our timing wasn’t good. We didn’t deal with the physicality. 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 and then we got a little better service and capitalized on them. It was just a sloppy game overall.”

To call Wednesday’s game physical is probably an understatement. After the USMNT took a 2-0 lead into halftime on goals from Omar Gonzalez and Eric Lichaj, El Salvador resorted to some dirty antics in the second half, biting not one but two US players.

Afterwards, Arena told reporters he thought someone should have been sent off. And asked if he thought his team could maybe learn from a game like this, the US coach was blunt.

“I don’t think so,” Arena said. “Games shouldn’t look like that. Too many fouls. Time wasting. Players falling on the ground. It doesn’t prepare us for big games.”

The US certainly have a big game looming Saturday as they're set to face a Costa Rica team that routed them 4-0 in a World Cup qualifier this past November.

And they know their Gold Cup run may end vs. Los Ticos in the semifinals if they once again come out slow and don’t, as striker Jozy Altidore put it, “put a stamp on the game.”

“Look, I think this was one of the better Salvador teams I’ve seen since I’ve been part of the national team,” said Altidore, who was on the wrong end of one of the bites – and nipple twists. “They gave us their best in the first 35-40 minutes but we rebounded well. We can’t be coming out flat like that. As games get tougher good, a good Costa Rica team will punish you early on for coming out like that.”

Along with Tim Howard, Clint Dempsey and Michael Bradley, Altidore was one of the big guns Arena brought in for the knockout round, hoping the longtime USMNT stars could elevate the team after a somewhat unconvincing showing in group play.

But even though Bradley and Dempsey came through with pretty assists and Howard had a nice early save, Arena thought the team “looked tired” and out of sorts for much of the hot night in Philly.

“I think our backline for the most part played OK,” Arena said. “I think Michael Bradley and Darlington Nagbe played very well. It was a very good goal by Omar and Lichaj … and at times, we passed the ball pretty well. But we weren’t clean in the last part of the field. We have to do better.”