Megan Rapinoe scored twice and the United States overcame early defensive shakiness to beat Australia 3-1 Monday night in the Americans' opener at the Women's World Cup.
Christen Press also scored for the second-ranked U.S., which is seeking its third World Cup title and first since 1999.
Lisa De Vanna had tied the score midway through the first half for Australia, beating controversial American goalkeeper Hope Solo.
"Obviously, we were a bit nervous," Rapinoe said. "Couldn't play a lot worse at times."
U.S. star forward Alex Morgan, sidelined by a bone bruise in her left knee, entered in the 79th minute in her first game action with April 11 with her Portland club.
Rapinoe scored in the 12th minute for the Americans, Press put the U.S. ahead for good in the 61st, and Rapinoe added her 31st international goal in the 78th, the first two-goal game at the World Cup for the Americans since Abby Wambach against Norway in 2007.
The U.S., which won the title in 1991 and '99, improved to 5-0-2 in World Cup openers and 23-0-2 in all matches against Australia. The game was televised in prime time on network television back home, where large numbers of fans tuned in last year for the men's World Cup in Brazil.
"Couldn't be prouder to have the women of Team #USA representing us in stars, stripes, and shin guards. Good luck," Democratic president candidate Hillary Clinton tweeted.
In the absence of the 25-year-old Morgan, 35-year-old Abby Wambach and Canada-born Sydney Leroux started up top against the No. 10 Matildas, whose best World Cup finish was sixth in 2007
While the American women have won three straight Olympic gold medals, the third World Cup title has eluded them. They lost the 2011 final to Japan on penalty kicks.
The field has expanded from 16 teams to 24 this year, and the Americans' next match in Group D will be Friday against Sweden and former U.S. coach Pia Sundhage. They finish group play on June 16 against Nigeria, which tied Sweden 3-3 in the opener of Monday's doubleheader.
The World Cup is being played as FIFA deals with a scandal which U.S. prosecutors allege involves more then $150 million in bribes. FIFA President Sepp Blatter, who is not at the tournament, announced last week that he plans to resign.
Controversy also hangs over the U.S. team. Solo started a day after an ESPN report revealed new details about her arrest last June in Washington state on domestic violence charges.
The U.S. team has defended Solo in the face of the allegations. The charges were dismissed by a Kirkland, Washington, judge earlier this year, but prosecutors told ESPN there is an appeal scheduled.
"That was a long time ago. I'll be honest, we've moved on," coach Jill Ellis. "She's been a fantastic player and teammate. None of that has even resonated with us, and I'm sure many of the players aren't aware of it."
Solo was tested in the fifth minutem, when she tipped Emily Van Egmond's shot off the crossbar and over. She made another save on Michelle Heyman in the 13th.
Rapinoe's kick from the top of the penalty area deflected off an Australia's Laura Alleway past goalkeeper Melissa Barbieri.
But De Vanna tied it when she facing off with Solo and slotted the ball inside the near post for her 36th goal in 100th international appearance appears
Press scored off a cross from Leroux in the 61st minute. When Press was subbed off seven minutes later she was given a hearty ovation from the crowd of 31,148, which overwhelmingly sided with the Americans. It was her first career World Cup goal.
Nigeria 3, Sweden 3: Francisca Ordega’s 87th-minute goal pulled Nigeria into a tie with Sweden in Winnipeg, Manitoba.
Linda Sembrant came off the bench to put Sweden ahead 3-2 before Ordega’s drive sailed between goalkeeper Hedvig Lindahl’s legs.
While Ordega celebrated with her teammates, Nigeria coach Edwin Okon dropped to his knees and kissed the turf on the sidelines.
Nilla Fischer put Sweden up 2-0 in the first half with a goal in the 31st minute after Nigeria conceded an own goal. Nigeria evened it in the second half when Ngozi Okobi and Asisat Oshoala scored in a three-minute span.
It was the tournament opener for both teams, who are in Group D along with the United States and Australia. An expanded field of 24 teams is playing in the monthlong World Cup.
Fifth-ranked Sweden, under former U.S. coach Pia Sundhage, faces her former team on Friday in one of the most anticipated matches of the group stage.
Cameroon 6, Ecuador 0: Cameroon scored three goals in a nine-minute stretch late in the first half and routed Ecuador 6-0 at Vancouver, British Columbia, in the Women's World Cup debuts for both nations.
Gaelle Enganamouit had a hat trick for 53rd-ranked Cameroon, which converted three penalty kicks. Enganamouit scored in the 36th and 73rd minutes, then got a penalty kick in the fourth minute of stoppage time.
Madeleine Ngono Mani put Les Lionnes ahead in the 34th minute, and captain Christine Manie's penalty kick made it 3-0 in the 44th.
Aboudi Onguene converted a penalty kick in the 79th,
Ligia Moreira of 48th-ranked Ecuador was given a red card for a foul in the 66th minute.
Cameroon plays defending champion Japan on Friday, and Ecuador meets Switzerland next.