The game changed in the 30th minute when Marco Urena scored the first of two goals. He clinched the win in the 82nd minute after Geoff Cameron, the USA's most experienced defender, turned the ball over.
First goal: 'We got split with our center backs'
Arena was missing only two starters -- both on the backline. Graham Zusi and Tim Ream replaced DeAndre Yedlin and John Brooks. Ream came in for a lot of criticism, but Arena said he was solid.
On Urena's first goal, Ream and Michael Bradley pushed Urena wide after Bryan Ruiz found Urena following a long clearance from Tim Howard in goal.
"It didn't look like he got much on the shot," said Arena of Urena. "Tim [Howard] perhaps lost his angle in the goal and [Urena] was able to roll it in. The play developed when Ruiz handled the ball in the middle of the center of the field, and the play went on and we got split with our center backs, which shouldn't happen."
Bradley-Nagbe pairing: 'I thought Darlington and Michael had solid games"
The one tactical wrinkle Arena threw out was inserting Darlington Nagbe with Bradley in midfield.
"Darlington and Michael were not the problems in our game tonight," Arena said. "The backline made some mistakes. We didn't come up with any big saves. Our attack players weren't dangerous on the night. I thought Darlington and Michael had solid games."
Pulisic: 'He had a tough game'
Christian Pulisic was pushed wide and failed to have an impact on the game. His best chance was stopped spectacularly by keeper Keylor Navas in the 67th minute.
"He had a tough game today," Arena said. "They paid a lot of attention to him. You could see early in the game that they always sent a second player to him. He got a little frustrated."
Tico tactics: 'They did a good job'
Arena gave a tip of the hat to the Ticos for their game plan.
"They came out with a very aggressive posture and pressed us up the field and, after conceding that first goal, they weren't going to come out a whole lot," Arena said. "We had to try and break down seven, eight players for long periods of the game. They did a good job. Navas made one very good save. We had a couple of plays where we have to put the ball in the back of the net and it's 1-0. We didn't do that. And we made a big mistake turning the ball over for the second goal."