It was just a few moments after Sanya Richards-Ross crossed the finish line first in the final USA vs. the World race at the Penn Relays that the public-address announcer at Franklin Field summed up the cloudy and cold afternoon a bit haughtily, but honestly.

"That's USA six, the World nothing," he said.

"Yes, I heard that," Richards-Ross said Saturday after the U.S. women won the 4x400-meter relay to complete a clean sweep of the events featuring athletes from 21 countries, many of whom have competed in the Olympics and the World Track and Field Championships.

"It was exciting to cross the line and kind of finish it off for Team USA. It was amazing. It's never been done before. Usually, the Jamaicans give us some trouble. So it was very, very exciting. I felt that spirit with my teammates all day, that everybody came out here to do a fantastic job and really set the tone going into London. So it was a great thrill for me to hear that."

Bershawn Jackson, a member of the men's winning 4x400 team, said the U.S. sweep was a positive sign.

"We're heading in the right direction toward London," Jackson said, referring to the 2012 Olympics. "But it's not just London. The hardest meet in the world is the Olympic trials. So this was good preparation. It keeps us thriving, and the fact that America came out on top, 6-0, that says: 'America is coming at you.' "

The U.S. women, with Allyson Felix running the second leg on both teams, set carnival records in the 4x100 (42.19 seconds) and 4x400 (3 minutes, 21.18 seconds). Felix, who excels at 100, 200, and 400 meters, has a decision to make as to what events she'll run in the trials, but she was pleased with Saturday.

"It was an honor to be part of both relays," she said. "For me right now, I feel my speed is really strong. I definitely felt strong on my 4x100. And I feel my 400 will come around, but I just wanted to get the baton around and keep the lead. I felt good on both relays. It's hard to say which one was better."

The women's sprint medley, with Maggie Vessey coming on strong on the 800-meter anchor leg, captured its first victory since 2007, in 3:42.85. Vessey ran an anchor leg of 2:02.6.

The U.S. men got off to a great start with Walter Dix anchoring the winning 4x100 team in 38.40. Leo Manzano outkicked veteran teammate Bernard Lagat in an all-American duel to win the distance medley in 9:19.31, the first U.S. win in the DMR ever at Penn.

In their final race, the U.S. men, anchored by Lashawn Merritt, blazed to victory in the 4x400 in 3:00.15.

"To run three minutes at this point of the season in this cold weather, that's pretty good," said Jackson, whose individual event is the 400-meter hurdles.

"For us, this is a confidence boost. Our first race is always pretty nerve-racking. We train hard, but you don't particularly know where you're at. But this shows us we're going in the right direction."

Khadevis Robinson, who ran the 800 leg on the winning distance-medley team, noted, however, that the coming U.S. Olympic trials and the London Olympics will be more difficult, as will the competition.

"We all know that in about a month or month and a half from now, everybody is going to bring their A game to make the Olympic trials," he said. "As much as you gain confidence after a win, when the trials come, it's all new, and you have to bring your A game again. When the Olympics come, you're going to see people from all sorts of countries run all sorts of times, so you have to refocus."

Contact Joe Juliano at 215-854-4494 or jjuliano@phillynews.com, or follow on Twitter @joejulesinq.