BARCELONA, Spain — The opening day of the swimming world championships could have doubled for a Trojan Swim Club meet.

American swimmer Haley Anderson, a recent graduate of the University of Southern California, won the first gold medal of the championships in the 5-kilometer open water and USC-based Oussama Mellouli of Tunisia won the men's event.

"It's a great job for the Trojans today," Mellouli said, thanking his American coaches Catherine Vogt, Jon Urbanchek and Dave Salo. "It's an awesome group."

Anderson was on the U.S. team a few times with Fran Crippen, who died during a sweltering 10K race in the United Arab Emirates in October 2010.

"Fran taught us to be great competitors," Anderson said. "We all learned from Fran and take his memory with us to all open water competitions and live like he lived."

The course ran along the docks, giving spectators a good view of the race in sunny conditions in 75-degree waters and air temperature of 86 degrees.

China's Wu Minxia and Shi Tingmao won the first diving gold medal, earning Wu a record sixth world title in the women's 3-meter synchronized springboard.

The pair's almost flawless execution of all five dives framed by the dramatic backdrop of Barcelona's skyline gave them the top total score of 338.40 points.

Italy's Tania Cagnotto and Francesca Dallape claimed silver with 307.80, while Canada's Pamela Ware and Jennifer Abel took bronze with 292.08.

Wu has won nine world or Olympic gold medals in the 3-meter synchronized springboard. The only major title to escape her was the 2005 world championship when she didn't compete in the event.

Svetlana Romashina won gold synchronized swimming for the solo technical event. Her standout Russian teammate Natalia Ischenko is taking the year off because she's pregnant.

Huang Zuechen of China took silver, and Ona Carbonell took bronze to give host Spain its first medal of the championships.

Romashina earned the 11th world title of her career, to go with her three Olympic golds.

Down at Barcelona's harbor, Anderson's victory erased the bitter disappointment of missing selection for her favored event.

A silver medalist in last year's 10K Olympic race, Anderson finished only eighth in that event at U.S. trials in May on the same day of her graduation from USC. Her only chance to qualify came down to winning the 5K days later, which she did.

Now she has an even bigger title.

"I didn't walk at graduation and I didn't do well in the 10K so it was a pretty tough day," Anderson said. "But I knew if wanted to make the worlds team I had to win the 5K. There really was no other option. I had to put that race out of mind and just win the 5K. I went for it in that 5K to make the team and I've been focused on this 5K ever since then."

Anderson edged Poliana Okimoto of Brazil in a sprint finish, clocking 56 minutes, 34.2 seconds, 0.02 ahead of Okimoto. Another Brazilian, Ana Marcela Cunha, won a group sprint for third and finished 10.5 seconds behind.

Anderson trains under Vogt at USC, and Vogt is the U.S. open water head coach for these championships.

"She wanted to be out front and be smooth and strong and have some good closing speed and she did exactly what we talked about," Vogt said. "She felt like she wanted to take advantage of her event here."

At last year's London Games, Vogt was on Tunisia's staff and coached Mellouli to gold in the 10K.

Having started purely as a pool swimmer, Mellouli's sprinting ability is what sets him apart in the open water. That was evident as he surged ahead of an elite group of rivals as soon as he got within the ropes outlining the finish area.

"I was hoping they wouldn't stay with me," Mellouli said. "Once I put the jets on I was able to take off, finish the race and take the win."

Mellouli clocked 53 minutes, 30.4 seconds. Eric Hedlin of Canada took silver, 1.2 seconds behind, and five-time world champion Thomas Lurz of Germany finished third, 1.8 back.

Including the open water worlds, Lurz had won the 5K title seven consecutive times.

"I knew in the last 50 meters I would not win," Lurz said. "(Mellouli) swims the 100 free five seconds faster than me or more. This is the problem."

Besides the 10K, Mellouli also took bronze in the 1,500-meter freestyle in London to become the first swimmer to win medals in both the pool and open water at the same Olympics. And he won the 1,500 at the 2008 Beijing Games.

The 29-year-old Mellouli had planned to retire after the London Games but he changed his mind a few months later. He only began training again six months ago.

"This year was supposed to be a year off for me," he said. "So to come back here after a solid two months of training and to be on top of the world is quite exciting for me."