[USA 23] Whether by design or not, U.S. coach Bob Bradley has given his three opponents in Group C a few variations to ponder. The U.S. midfield could take several radically different looks, depending on whom Bradley chooses to play in the middle, presuming Landon Donovan and Clint Dempsey man the wide slots. And even if Michael Bradley is a constant, his possible partners – Maurice Edu, Jose Francisco Torres, Ricardo Clark, Benny Feilhaber – play very differently.

So, too, can the forward line, where Jozy Altidore could be paired with Robbie Findley, Herculez Gomez, Edson Buddle, or possibly Clint Dempsey, who started up top Saturday against Turkey before dropping into midfield for the second half.

Bob Bradley can again utilize up to six substitutes Saturday (8:30 a.m. ET, ESPN2, Galavision) in the final warm-up match against Australia in Roodepoort to get a few final looks at certain players, but he’s expressed the possibility of starting his presumed starting XI; he might also choose to give more players a full 90 minutes than he has in the past two matches.

These myriad variations won't mean much, however, if the USA can’t stay tight at the back. Since qualifying for the 2010 World Cup in October, the Americans have conceded at least three goals three times: in losses to Denmark (3-1), Honduras (3-1), and Czech Republic (4-2).

Friendlies are for experimentation, yet regardless of personnel or opponent, that’s simply too many goals at the wrong end.

"First off, we need to sharpen up defensively," said defender and captain Carlos Bocanegra at a press conference Tuesday, the first one staged since the team’s arrival Monday night after a 17-hour flight, including a refueling stop in Senegal, from Washington, D.C. "I think that could be improved on. We're trying to gel as a team and peak come June 12. The thing that sticks out to me at the moment is to be a bit better defensively and have a better team shape from the back to toward the front.”

Bradley named only seven defenders to the squad, and at least three seem to be lagging behind as the World Cup approaches. Jonathan Bornstein didn’t look secure against either the Czech Republic or Turkey, Jonathan Spector labored for a half Saturday before being replaced, and Jay DeMerit – bothered by an eye irritation and an abdominal strain – is off his game.

Bocanegra expressed relief at playing 75 minutes against Turkey in his first competitive stint since undergoing sports hernia surgery in Munich May 5.

"I feel good. It was nice to get the 75 minutes,” said Bocanegra. “They’ve done a good job, the trainers and the coaches, with my program and easing me into it and not just throwing me out there full blast. I held up well. I just need to work on sharpening up the last five percent or so.”

Oguchi Onyewu played the second half Saturday in his just second appearance since rupturing his patellar tendon Oct. 14 against Costa Rica.

Steve Cherundolo missed more than a month of the German Bundesliga season with a shoulder injury, but returned in March and played a strong second half to help the U.S. overturn a 1-0 deficit against Turkey. Clarence Goodson sat out the Turkey game after marring an otherwise strong showing in the Czech Republic encounter with a defensive miscue that led to the winning goal.

After starting in midfield and scoring the goal that gave the U.S. a lead 1-0 against Czech Republic, Edu dropped into central defense for the second half. The USA lost control of midfield, and in stoppage time the Czechs scored their final goal after a ball skipped off the top of Edu’s head and fell for Tomas Necid to break through and beat keeper Brad Guzan.

“It's a position I played at the Olympics so it is familiar,” said Edu of his experience in 2008. "I got a little bit tired but I felt pretty comfortable back there. I played quite a bit in the back and the coaches have said they might play me in that position if need be.”

Edu in the back line would give the Americans yet another defensive version and alter the midfield as well.

The 74-room Irene Country Lodge, north of Johannesburg and south of Pretoria, is the team’s base camp. The USA will train at nearby Pilditch Stadium in Pretoria, a 5,000-capacity facility that is very familiar.

"It’s a place where I think we can really concentrate on our work," said Coach Bradley. "We trained at Pilditch last year during Confederations Cup and the field was quite good then and they tell me it’s even better this year. So, I think, we’ve done a good job in terms of getting these things squared away and it gives us the best chance for success.”

With 10 days to go before the opener June 12 against England, which dropped Arsenal winger Theo Walcott from its 23-man squad in a surprising move, the U.S. team scheduled a light training session Tuesday.

"The team is excited to get started," said Bradley. "The first training session after we travel is always a shorter one, where we just try to get everybody going again but you can tell there is a good level of excitement to get started."