DeMar DeRozan grabs a rebound in front of Serbia’s Nikola Kalinic and Bogdan Bogdanovic. (Marko Djurica/Reuters)

So this is how it’s going to be.

If the United States men’s basketball team wants to win a gold medal, if it wants to avoid the ignominy of falling short for the second time in the past four Olympics with NBA players, it had better prepare to win a lot of fidgety games. It had better get used to surviving, like it did Friday night in a 94-91 victory over Serbia that wasn’t certain until Bogdan Bogdanovic missed a three-point attempt in the final second.

The rest of the world isn’t awestruck, not by this team. Despite still possessing superior talent, Team USA looks flawed and vulnerable and plays the way you’d expect a squad formed just last month to play. And the competition is organized, rigid and full of offensive ingenuity. That’s why Australia scared the Americans into humility before the they prevailed, 98-88, on Wednesday. And that’s why the United States couldn’t simply dominate Serbia and prove the previous game was a fluke.

Reality has set in for the U.S. players. After two blowouts, they’ve played two close games. After building an 18-point lead in the first quarter against Serbia, they were a shot away from being forced into overtime at Carioca Arena 1.

This is how it’s going to be: difficult, nerve-wracking, more taxing than they imagined.

The U.S. men's basketball team heads to the Rio Olympics as the favorite to win gold, even without the reigning regular season and NBA Finals MVPs. (Jayne Orenstein/The Washington Post)

“As good as we are, if we continue to keep playing like this, these games are going to be even tougher,” said forward Paul George, who had 12 points against Serbia.

Defense and point-guard play have been glaring issues of late. Australia exposed the defensive problems, sharing the ball and moving without it, punishing the Americans for every mistake. Serbia continued the trend by shooting 52 percent. Serbian center Nikola Jokic, who also plays for the Denver Nuggets, scored 25 points on 11-of-15 shooting. Team USA also couldn’t handle guard Milos Teodosic, who finished with 18 points and six assists. And center Miroslav Raduljica was a problematic physical presence, scoring 18 points in 15 minutes before foul trouble took him out of the game.

“As good as we are offensively, defensively is where we’ve got to really man up,” George said. “What’s killing us right now is pick-and-roll play and guys slipping out of it. It’s a different game. Euros guys are phenomenal with movement and cuts and playing as a group. That’s one thing they do well in our league. It’s a different game for us.”

The United States (4-0 in Group A) came ready to play. It scored the game’s first nine points and built a 23-5 lead. DeMarcus Cousins spun in the open court and soared for a dunk. Klay Thompson, who has been struggling, hit his first three-point attempt. DeAndre Jordan caught lobs from all directions. It seemed like a blowout was in the works, like the Americans were about to show that the Australia game was an aberration.

Then the defense fall apart, and in the second quarter, the game got chippy as the United States was called for two of the game’s three technical fouls. The offense wasn’t fluid, either. Team USA has two good lead guards on the roster — Kyrie Irving, who scored a team-high 15 points, and Kyle Lowry — but neither is the classic, pass-first playmaker. Neither dances between scoring and playmaking as well as Steph Curry and Russell Westbrook, the NBA’s best two point guards, who chose not to play in the Olympics.

During critical possessions, the United States looked disjointed. Its best player, Kevin Durant, scored 12 points, but he took only four shots and had just one field goal attempt in the first 31/2 quarters. With Team USA up by three with nearly a minute remaining, it needed one good shot to ice the game, but Irving dribbled the entire possession and took a 10-foot runner that ricocheted off the backboard.

“We’re still scoring close to 100 points, but we’re taking 1-on-5 shots, and we’re too good for that,” George said. “The toughest part is, each and every one of us is confident with the ball in our hands that we can make those shots. It just comes down to a trust factor, not letting one guy have that feeling that he has to do it alone.”

Afterward, Coach Mike Krzyzewski didn’t overreact. He mostly praised Serbia and continued to emphasize the strength of the competition in this tournament. Still, Serbia entered the game with two losses in group play. Australia had beaten Serbia 95-80 earlier in the tournament. But the United States found a determined team.

“We thought we had it going a little bit in the first half,” guard DeMar DeRozan said. “But with a team like Serbia, they weren’t going to lay down. They weren’t going to put their head down, and they fought. We’ve got to understand, if we get up big like that early on, we’ve got to pick it up as well, like we’re losing, because nobody is going to lay down.”

For the rest of this tournament, no one will lie down for Team USA. The question is how an American team with 10 first-time Olympians will hold up.