Michael Phelps almost failed to qualify for the final in the first of his seven events, and Olympic champion Park Tae-hwan was reinstated after being disqualified for a false start in a dramatic opening to swimming at the London Games on Saturday.
"That one didn't feel too good," Phelps said after squeaking into the final in the 400-meter individual medley by seven-hundredths of a second.
Park touched the wall first in his 400 freestyle heat and was surprised by his disqualification, saying, "I don't know why" after he walked off the deck.
South Korea appealed to swimming's governing body, which reinstated Park after a video review, FINA executive director Cornel Marculescu told The Associated Press.
Park and Phelps were not the only surprises of the morning at the Aquatics Centre, where Queen Elizabeth appeared briefly. Paul Biedermann of Germany, the world-record holder in the 200-meter freestyle, failed to make the final.
"That's the Olympics," said Canadian Ryan Cochrane, who initially took the last spot in the 400 freestyle final but was knocked out when Park was reinstated. "It's always a surprise, every single heat. You just have to focus on your own race."
In Beijing, Park became South Korea's first swimming gold medalist. He also won the world title in Shanghai last year.
Phelps, the two-time defending Olympic champion, won his 400 IM heat in 4 minutes, 13.33 seconds with a time that was well off his world record of 4:03.84 set four years ago, when he won a record eight gold medals.
But it was only good enough to secure the last spot in the evening final, when Phelps will swim in Lane 8 instead of the middle of the pool. He breathes to his right, so he won't see the field coming home.
"The only thing that matters is just getting a spot in," he said. "You can't win the gold medal from the morning."
In the 400 IM, Kosuke Hagino of Japan led the way in 4:10.01, a national record. Chad le Clos of South Africa was second at 4:12.24, and Ryan Lochte of the United States advanced in third at 4:12.35.
Phelps' time was just fast enough to keep Laszlo Cseh of Hungary, the silver medalist in Beijing, out of the final. Cseh was ninth overall after leading Phelps during their heat before the American closed on the last lap of freestyle to beat him to the wall.
"I didn't expect those guys to go that fast in their heat," Phelps said. "I was slower this morning than I was four years ago."
Phelps' time in the grueling event, which he had vowed not to swim again after Beijing, took some of the luster off what was expected to be a showdown between him and Lochte for gold.
"You can't count him out," Lochte said, referring to Phelps. "Even though he just squeaked in eighth, he's a racer. We're going to do everything we can to go 1-2 tonight."
Lochte, the bronze medalist in Beijing, has won the 400 IM at the last two world championships.
"My first race is always the worst one," he said. "I'm glad I got the cobwebs out."
Kosuke Kitajima of Japan opened his bid to become the first male swimmer to win the same individual event at three consecutive Olympics. He qualified second-quickest in the 100 breaststroke at 59.63 seconds behind Christian Sprenger of Australia in 59.62.
"I don't have any pressure, I just try to enjoy," Kitajima said. "It felt so good. It was good for my first race. I will try to improve in the semifinals."
Giedrius Titenis of Lithuania was third at 59.68. Twelve of the 16 swimmers who reached the semifinals swam under 1 minute.
American Brendan Hansen, the 2004 Olympic silver medalist who was fourth in Beijing, qualified 10th at 59.93. Teammate Eric Shanteau was 11th at 59.96.
"Everybody seemed to be going out real fast in the first 50," Hansen said. "I wanted to come home strong. I let everybody know that last 50 is going to be there. This race is going to be won in the last 15 meters."
Missing from the 100 breast was Alexander Dale Oen of Norway, the world champion who would have been a medal contender in these games. He died in April of cardiac arrest at 26 during a training camp in Arizona.
"We're carrying him with us all the time," Sara Nordenstam of Norway said after her heat in the 400 IM. "We have our own way of honoring him - that's swimming fast and remembering him and remember everything that he taught us and go for the goals that we set together."
Dana Vollmer had the fastest qualifying time in the 100 butterfly at 56.25, setting American and Olympic records, to lead 16 women into the evening semifinals.
"I'm really happy with how fast it was and I think it's only going to get faster," she said. "That's kind of a confidence-booster. I'm ready to go."
Lu Ying of China was second in 57.17 and Australian Alicia Coutts was third at 57.36. Sarah Sjostrom of Sweden, the world record holder, was fourth at 57.45.
American Claire Donahue moved on in seventh, while British teammates Francesca Hall and Ellen Gandy were eighth and ninth.
Jess Schipper of Australia, the bronze medalist four years ago, was 24th and missed the semifinals by eight spots.
In the 400 free, Sun Yang of China qualified fastest in 3:45.07. American Peter Vanderkaay was second at 3:45.80, followed by his teammates Conor Dwyer in 3:46.24.
Biedermann washed out for the second straight Olympics. He also didn't make it out of the heats in Beijing. He set the world record at the 2009 world meet in Rome at the height of the high-tech body suit craze. Those suits have since been banned.
"It wasn't so good," he said. "I wanted to lead from the front, but I couldn't hold it."
World champion Elizabeth Beisel of the United States qualified fastest in the women's 400 IM at 4:31.68. Ye Shiwen of China was second at 4:31.73.
Katinka Hosszu of Hungary, who trains at the University of Southern California, was third in 4:33.77. Britain's Hannah Miley got the loudest cheers while advancing to the final in sixth.
Rice, a triple gold medalist in Beijing who has struggled with shoulder injuries the last three years, was seventh.
"Whew! That took quite a bit out of me," Rice said. "I know that I've done everything I could. I'm pretty at peace with the fact that I'm just going to get in there and do my thing and see what happens."
American Caitlin Leverenz got the last spot in the eight-woman final.
Australia had the fastest qualifying time in the 4x100 free relay. Emily Seebohm, Brittany Elmslie, Yolane Kukla and Libby Trickett were timed in 3:36.34.
The U.S. team of Lia Neal, Amanda Weir, Natalie Coughlin and Allison Schmitt was second at 3:36.53.
"I think we did our goal of putting us in a good spot for tonight, which was the main thing," said Coughlin, who has 11 career medals but didn't qualify to swim any individual events in London.
She has a chance to join Dara Torres and Jenny Thompson as the most decorated U.S. female Olympian if the Americans earn a medal in the evening final, whether or not Coughlin returns to swim. Torres and Thompson both won 12 medals.
The defending champion Dutch team of Marleen Veldhuis, Inge Dekker, Hinkelien Schreuder and Femke Heemskerk was third at 3:37.76.
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