"The 50.71 is okay for now but there's a lot of improvement to make before London," said Phelps who is using the championships to gauge what he needs to do to prepare for his final Games before retirement.

"I'm not in the right shape physically, I want to be faster. I will watch some races and think about how I can be faster," he told reporters.

"It shows I'm going in the right direction and making progress ... this is going to be a lot of help that I can work on next year," added Phelps who landed an unprecedented eight golds at the 2008 Beijing Olympics.

Teenager Melissa Franklin, on her debut at the championships, almost stole the spotlight from Phelps when she won two golds in different disciplines.

It was the first time the U.S. had won the medley relay since 1998. China finished second and Olympic champions Australia took bronze in the final race of the day.

"It's unbelievable," said an excited Franklin. "I'm really happy."

BRITISH GOLD

The Briton, who took silver behind Federica Pellegrini in the 400 freestyle last weekend, battled with 2009 Rome world champion Lotte Friis stroke for stroke before piping the Dane on Saturday.

Friis led on virtually each lap. Adlington made her move at the halfway mark before her rival surged again to move in front for the next 300 meters.

The 24-year-old, who also won the 50 butterfly on Monday, was cleared to compete just three days before the championships when the Court of Arbitration for Sport ruled he had taken "sufficient precautions" in handling his supplements.

Cielo had said the supplements were contaminated and were the cause of a positive test for the banned diuretic furosemide.

"I was tense during the entire week. But I'm satisfied with the way I overcame everything. That shows a lot of mental control," Cielo said.

Dutchwoman Inge Dekker was first in the women's 50 butterfly, edging out world record holder Therese Alshammar of Sweden.

"The 50 meters is always exciting," said Dekker. "Anyone can win it -- this time it is me."

(additional reporting by Soo Ai Peng)

(Editing by Tony Jimenez)