Meghan Klingenberg figured she could go above and beyond to further build team camaraderie, and it involved a box of beautiful gourmet doughnuts for her teammates before a recent World Cup tuneup.

Such gestures mean a lot for a group still getting to know each other.

With each match the Americans play and through every rigorous training session, Klingenberg and the defense become more comfortable together on a new-look back line ahead of their World Cup opener 2 1/2 weeks from now against Australia in Winnipeg.

"Step 1 to becoming the most popular girl on the team," wrote Klingenberg, who posted on Twitter a photo of the doughnuts from a popular San Jose spot.

The U.S. foursome that started in a 5-1 victory against Mexico in last weekend's send-off match in Carson featured nobody with more than 80 appearances for the national team, yet that certainly doesn't seem to have coach Jill Ellis overly concerned heading to Canada. Especially with veteran defender and captain Christie Rampone helping lead this young group in her fifth World Cup. She has the second-most international caps in U.S. women's soccer history with 305 behind Kristine Lilly and will turn 40 during the tournament, too.

Ali Krieger started all six matches of the 2011 tournament in Germany, while Becky Sauerbrunn earned a start. Add newcomer Julie Johnston and Klingenberg to the mix and Ellis acknowledges she has a uniquely skilled defense that loves to push forward on the attack whenever possible.

"We're asking more of them in the attack than we have in the past," Ellis said. "But I certainly think that defensively we're coming together. We read the game collectively very well. I still think individually there are things we can improve upon."

Goalkeeper Hope Solo has needed time to adjust to different players' tendencies as Ellis mixed and matched combinations to find her best lineup heading into the World Cup Group D opener on June 8.

Everybody involved understands there is unfinished business after the United States lost to Japan on penalty kicks in the 2011 World Cup final.

"Each game we're ironing out the details in the back. We have our clean sheets," Krieger said. "As of right now, we're golden. We've done really well together and we have a great understanding, a great communication in the back four. It's super strong. We also have so much depth for a back line. Anybody that has to come in and jump in is right there on the same page, and I think we've done such a great job in the last two games to solidify that."

The second-ranked U.S. team (7-1-1) has allowed just one goal over its last six games, and that was to Mexico. The Americans have eight shutouts dating to a 7-0 victory against Argentina on Dec. 18.

It hasn't seemed to matter much the personnel Ellis chooses.

Johnston earned her spot after filling in for the injured Rampone and Whitney Engen at March's Algarve Cup in Portugal. She scored her first career goal for the Americans in a 2-0 win over France in the Algarve Cup final March 11.

Johnston played in just her 11th match for the Americans last weekend, after she scored in a third straight game with a goal against Ireland on May 10.

"She's a warrior. She's got great spirit," Ellis said. "She's got grit. She will sacrifice life and limb to stop a defender or block a shot."

What some of these women might lack in experience on soccer's biggest stage they are determined to make up for with their energy on both ends of the field.

No ball gets by them, they tell each other. No matter who is on the field together at any given time.

"Our back line, our back four, everybody, is so easy to play with because we've been doing it a long time now," Klingenberg said. "It really doesn't matter who you're putting in. The way that we can read each other and rely on each other is really special. You get a rapport playing together. I feel like they totally have my back, same with Hope and all the rest of the keepers. When you can feel like that with your team you know it's good going forward. It's great."

Klingenberg has played alongside Sauerbrunn regularly and previously with Engen on the Houston Dash.

Krieger had a scare last month when she sustained a concussion with her Washington Spirit team. She has been using a protective headband, which only requires a slight adjustment after a header.

Solo sees strides as she watches the group in front of her. The Americans' final World Cup tuneup is May 30 against South Korea in Harrison, New Jersey.

"It's a learning process, but it's been a few years now, not necessarily working with the exact back line but with the same teammates," Solo said. "I'm comfortable and I'm really confident with my back line right now."

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AP Sports Writer Anne M. Peterson contributed to this story.