“It was so cold that I didn’t push too much at the start, but I am happy with that,” said the 28-year-old Jamaican.
“We all want to get the best start but when there’s false starts it puts you in a different zone. I was only going to do enough to win today (yesterday). I didn’t want to push too hard. I just wanted to get the win.”
Powell finished ahead of Jamaican teammates Nesta Carter (9.93sec) and Michael Frater (10.01sec) in a race where there were two disqualifications.
Powell, building up to the World Championships in South Korea from August 27 to September 3, had already thrown down the gauntlet to rivals including world record holder Usain Bolt by running the fastest 100m of the season in Lausanne last week.
He clocked 9.78sec, dipping under 9.8sec for the eighth time in his career.
Only double sprint World and Olympic champion Bolt (five times with a world record best of 9.58sec) and American Tyson Gay (five times with a best of 9.69sec) have run faster, while Carter, has also managed to time 9.78sec once in his career.
“At the Worlds I’m definitely going to win. I’m going for it and I’ll try not to disappoint,” added Powell.
In the triple jump, Phillips Idowu of Britain got the better of his great rival Teddy Thamgo of France with a leap of 17.54m.
Thamgo already had the best performance of the season when he recorded 17.91m in Switzerland, but yesterday he had to settle for fifth place with a poor 16.74m.
Despite the fresh conditions in Birmingham, two season-best performances were recorded.
In the men’s javelin, Norway’s Andreas Thorkildsen confirmed his number one status with a throw of 88.30m while Australia’s Sally Pierce set a season-leading 12.48sec in the women’s 100m hurdles.
The men’s 800m was won by the Sudanese Abubaker Kaki in a time of 1min 44.54sec, making the most of the absence of Kenyan runners including world record holder David Rudisha who is training for the world championships.
Britain’s Mo Farah won the 5,000m in 13min 06.14sec.
In the women’s 200m, American favourite Carmelita Jeter could only finish third in 22.62 seconds behind compatriots Bianca Knight (22.59sec) and Marshevet Myers (22.59sec).