Gatlin said on Saturday he was ready to break the world record if necessary and added that nothing Helsinki's unpredictable weather could throw up would stop him taking the title.
In the absence of Jamaica's injured world record holder Asafa Powell, the 23-year-old American was as good as his word and stormed to victory in 9.88 seconds on a cool but mercifully dry evening.
Powell's training partner Michael Frater finished second in 10.05 seconds ahead of defending champion Kim Collins of St Kitts and Nevis who clocked the same time.
"Even if Asafa had been in the race I'd have been number one," Gatlin said. "I'm the one who came to the big dance and stopped the show.
"I'm going to be the fastest man in the world also in the future. I am the Olympic champion and the world champion but I want Justin Gatlin to be the champion on everything.
Sweden's Carolina Kluft bounced back from a troubled first day to retain the heptathlon title ahead of former champion Eunice Barber in another demonstration of her unquenchable competitive spirit.
TOUGH TIME
The Olympic and defending world champion was hampered by an injured left ankle on Saturday and trailed Barber by two points overnight.
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The effort proved too much as Kluft first tracked the Frenchwoman and then overtook her on the final lap to finish with 6,887 points to Barber's 6,824.
"I had a tough time with injury," Kluft said. "It was hard. I didn't know how Eunice was going to run. I tried to see her all the time and tried do my best and when there was 200 left I just pushed it all the way I could."
Lithuanian Virgilijus Alekna showed similar competitive spirit to retain the men's world discus title with his final throw of 70.17 metres to overhaul Estonian Gerd Kanter.
"He put me under an awful lot of pressure," said Alekna. "It was do or die in the end. I always try to make the winning throw with my first attempt but today it didn't work."
In the morning session on the second day of the championships Russian Olimpiada Ivanova won the first of the day's five titles when she strode to victory in a world record one hour 25 minutes 41 seconds in the 20 km walk.
Ivanova, who has served a two-year drugs suspension, won $160,000 for her morning's work, including a $100,000 bonus for breaking the world record.
Trecia Smith completed an excellent evening for Jamaica by winning the women's triple jump to gather her first major title.
Twice world champion and title favourite Tatyana Lebedeva, who won the long jump gold in Athens, pulled out of the triple jump shortly before the start of competition. She had suffered an Achilles tendon injury in Oslo last month.
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