The men are trying to defend the gold medal they won at the 2008 Beijing Olympics, but three-time Olympian Clay Stanley said they try not to look at it that way.
"We don't feel like we need to defend our title," he said. "We see this as a new journey since Beijing. It's best not to think that way, and take every game as if it's your last."
The Americans are not considered a favorite in London despite a silver-medal finish in the recent FIVB World League tournament. But they were formidable against Serbia, which won the Olympic gold in Sydney in 2000 and finished fifth in Beijing in 2008.
Marko Podrascanin had 13 points, including two aces, for the Serbians.
"It was a good match. We fought hard and won in three straight, which is pretty much exactly what our game plan was to do," Anderson said. "We wanted to serve tough and put a lot of pressure on them, and I think we executed that pretty well."
Four years ago, the U.S. men went undefeated in Beijing, upsetting Brazil in the final. That team was coached by Hugh McCutcheon, whose father-in-law was stabbed to death at a Chinese tourist site just before the opening ceremony. The coach left the team for several matches to be with his family.
McCutcheon shifted to the U.S. women's team following Beijing, and Alan Knipe took a leave of absence as coach of Long Beach State to coach the men for London.
The U.S. is ranked No. 5 by volleyball's governing body. The team is in a difficult pool in London, joining top-ranked Brazil, perennial powerhouse Russia, Serbia, Germany and Tunisia. In the other pool are Italy, Poland, Argentina, Bulgaria, Australia and host Britain.
The U.S. jumped to an 18-7 lead in the first set and the public address announcer proclaimed it an "absolute mauling." David Lee spiked for set point.
Serbia went up 6-2 in the second set before the Americans rallied. The Serbians managed to hold off the Americans for three set points before a return error ended the set.
David Suxho's ace made it 15-7 in the third, and the Americans were on their way, drawing chants of "U-S-A!" from the crowd.
"It was a well-played match, and it was probably more the mindset of the players that got them through," Knipe said. "We did a really good job to maintain our composure when we were down in the second set."
Serbian wing spiker Milos Nikic gave credit to the United States for the victory.
"We didn't really get into it. We played well in parts, but we didn't keep our momentum," he said. "We can play better."
Since volleyball became an Olympic sport in 1964, the U.S. men have won three gold medals Los Angeles in 1984, Seoul in 1988 and Beijing in 2008. The men won the bronze in 1992.
In early matches Sunday, Bulgaria swept Britain, 25-18, 25-20, 26-24, and Russia defeated Germany 31-29, 25-18, 25-17. Australia, coached by Jon Uriarte, lost to Argentina 25-21, 25-22 25-20. Son Nicolas Uriarte is a setter on the Argentine team.
In the late matches, Poland defeated Italy 3-1 (21-25, 25-20, 25-23, 25-14), and Brazil swept Tunisia (25-17, 25-21, 25-18).
The Associated Press contributed to this article.