The former world record holder from Jamaica got off to good start running into a headwind at Crystal Palace, but most of the field stayed with him until the midway point. Instead of easing across the finish line for his second win this week, however, Powell had to keep pushing because the pack again caught up to make it close at the finish.
"The race did not quite go as expected but felt easy," Powell said. "A bit more work to do and everything should be fine for Beijing."
Powell, who has yet to win an Olympic gold medal, is expected to come up against world champion Tyson Gay and record holder Usain Bolt at the Beijing Games.
"There are a lot of people running fast at the moment and I don't see any one athlete as being my main competitor," Powell said. "The way I am running at the moment I feel I am in the best shape I have been in."
Bolt, Powell's Jamaican teammate, set the 100 record in May, running 9.72 in New York. He decided to skip the 100 in London and will run Sunday in the 200. He has also said he is still undecided about running in both the 100 and 200 in Beijing.
Powell beat Bolt in the 100 on Tuesday in Stockholm, running 9.88 to win.
"The Jamaicans are running quite well," Powell said.
Marc Burns of Trinidad and Tobago was second in 9.97 seconds, and Michael Frater of Britain was third in 10.00. Gay pulled out of the 100 in the London meet because he is still nursing a hamstring injury he picked up at the U.S. Olympic trials last month.
Yelena Isinbayeva struggled to get going in the women's pole vault, and then took three attempts at another word record.
The Russian, who won the event Friday with a jump of 4.93 meters, had three attempts at 5.04, one centimeter higher than her outdoor world record.
"I really felt I could jump a world record today," Isinbayeva said. "I was so close."
The third attempt nearly gave Isinbayeva her 23rd world record, but despite teetering on its perch for a moment, the bar fell to the ground.
"I've got one more competition then a rest for two weeks before Beijing," Isinbayeva said. "It's going to be a hard competition and it might be necessary to break a world record to win."
At her opening height, Isinbayeva needed all three attempts to clear 4.74.
Jenn Stuczynski, who finished second at 4.81, took two attempts at a world record after failing to clear 4.93 in her only chance. Anna Rogowska of Poland was third with a jump of 4.65.
"It started off pretty good but at the end I think I was trying too hard and I didn't go with what I had been working on in practice," said Stuczynski, who will represent the United States at the Olympics. "My preparations are going really well so I'm really disappointed in today's performance."
With the Beijing Games approaching, Jamaican sprinter Sherone Simpson showed she can keep pace by winning the women's 200 in 22.70.
"To get a win so close to the Olympics is very good psychologically," said Simpson, who was slowed by injuries for much of 2007. "My past two races weren't that good at all, so having this win against some good competition is a great boost for me."
Bianca Knight, a 19-year-old American, was second in 22.79, and Debbie Ferguson of the Bahamas was third in 22.84. World champion Allyson Felix of the United States was fourth in 23.00.
The Olympics open on Aug. 8, and Felix will be there to compete in the 200 despite failing to qualify for the U.S. team in the 100. She declined to speak to reporters after the race, and skipped the women's 400 relay.
World champion Christine Ohuruogu ran her fastest 400 this season, winning in 50.81.
In the men's mile, Shedrack Korir led all the way around the final lap to win in 3:54.68. The Kenyan held off Andrew Baddeley down the final stretch, with the Briton finishing in 3:54.76.
Bernard Lagat, the world champion in the 1,500 and 5,000 from the United States, was third in 3:55.20 for his first lost in 10 races this season.
"I'm going to make sure I don't lose again because if I lose the next one it means I lose gold," Lagat said. "I can't afford to lose the one that's coming up, the Olympics."
David Oliver of the United States won the 110 hurdles in 13.20. Anwar Moore of the United States was second in 13.52 and Stanislav Olijar was third in 13.57.
"Beijing is the race to be in," Oliver said. "I am feeling very confident. My chances are as good as anyone else."
Reese Hoffa won the shot put with a throw of 21.13, and American teammate Adam Nelson was second at 21.07. Tomasz Majewski of Poland was third with a throw of 20.97.
"I've got two weeks training now and I am feeling in great shape," said Hoffa, who has thrown 22.10 this season. "The distances weren't there tonight but the win will give me a lot of confidence for Beijing."
Kelly Sotherton of Britain leads the women's four-event challenge with 2,129 points. She won the long jump with a leap of 6.79 meters, and finished fourth in the 100 hurdles in 13.66.
Gi-Gi Johnson of the United States, who won the hurdles in 13.09, is second with 2,060 points, and Funmi Jimoh of the United States is third with 1,975.
