How well the Brazilians contain forwards Abby Wambach and Kristine Lilly and cope with tenacious left back Stephanie Lopez will be just as pivotal in the game's outcome.
The USA. has yet to concede a goal in this tournament playing 11 against 11; North Korea scored twice in the opener while a gash in Wambach's scalp was being stitched up. Brazil has scored 13 goals in its four matches while allowing just two, both to Australia in the quarterfinals.
Yet if past experience is any gauge, Osborne and Lopez should ask teammate Shannon Boxx not only for help subduing Marta, but also of what can be thrown at a World Cup neophyte in a semifinal.
Four years ago, the robust Boxx played solidly in the group matches and against Norway in the quarterfinals. Germany proved to be a tougher test, as its fluid, cohesive midfield play often left the U.S. midfielders chasing shadows. The Germans scored in the 15th minute on a corner kick and rode out several American attacks before punching in two late goals to win, 3-0.
A year later at the 2004 Olympic Games, a sharper and wiser Boxx patrolled the midfield as the Americans knocked off Germany in the semis and took the gold medal by beating Brazil, 2-1, in overtime.
Yet Brazil equalized in the 73rd minute with a mesmerizing dribble by Cristiane, who fed Pretinha for the tying goal.
Brazil hit the woodwork twice but Wambach scored the winner deep into overtime.
Since that game, four mainstays of the U.S. team -- Brandi Chastain, Mia Hamm, Julie Foudy, and Joy Fawcett -- have either retired or been ushered out of the picture.
That heartbreaking loss has simmered in Brazilian souls for more than three years. Those souls might have been distracted in the quarterfinal last weekend, when Brazil jumped out to a 2-0 lead yet needed Cristiane to nail a spectacular winner in the 75th minute after the scrappy Aussies fought back to tie the match.
Marta leads the team - and everyone else in the tournament except Ragnhild Gulbrandsen of Norway - with five goals, but Cristiane has four and four other Brazilians - including Pretinha - each have one. Marta, Cristiane and Formiga each have two assists.
This team is far more than just Marta. It can attack from many angles, carve open defenses with scything dribbles and combination passing, and its defense is formidable. She and her teammates are three years older and in most cases, three years better.
Lopez, 21, and Osborne, 24, are two of six players who made their U.S. debuts during the reign of Coach Greg Ryan, who took over the team in 2005. They played a combined 49 minutes that year. Now both are fixtures in the squad.
Osborne sat out the opener against North Korea but came into the lineup in the second group game against Sweden as Ryan opted for more bite in midfield. Lopez has played every minute. They are likely to be targeted by savvy opponents searching for a clumsy foul, a missed tackle, any sign of weakness.
"I wasn't nervous, I was more excited than anything," said Osborne after the Sweden match. "I've been training for this the past two years. I think I got all of my nerves out of the way during the national anthem, so once the whistle blew it was just fun from there."
Says Lopez, the youngest U.S. player and the same age as Marta: "The veteran players are consistent throughout a span of games and also within a game for all of the minutes. By having that consistency in my game the coaches don't have to worry if I'm going to zone off. That can't cross their minds."
Let the mind games begin.