Moscow - US sprinter English Gardner fired out a warning to defending world 100m champion Carmelita Jeter by topping the heats on Sunday, but will be hoping her inexperience on the big stage does not come back to haunt her.
Gardner was the shock winner of the US trials, clocking a personal best of 10.85sec in the process, with Jeter opting not to race because of the wildcard entry afforded her as champion.
And the 21-year-old, making her debut on the international stage in Moscow, did not hold back in her heat, as more experienced racers normally do in a bid to conserve their energy for the later semi-finals and final.
Instead, after an electrifying start, she scorched through the line in a very impressive 10.94sec, the sole sprinter to dip under the 11sec mark.
"I did everything my coach told me to do," Gardner said, denying she had exerted too much energy before Monday's semis.
"I wasn't running too fast. Somebody next to me could do anything they want. I'm doing what I have to do.
"I took care about my own race, my own lane."
Gardner added: "It's so exciting to be here and represent my team. I'm happy with my time and the fact that I executed.
"I've recently turned professional, but the transition was pretty easy. I think I've always had that pro mentality, even in college."
Jeter, 33, contented herself with second place behind US-based Ivorian Murielle Ahoure in the morning session's slowest heat.
Should the American make the podium, she would tie Merlene Ottey's record of being a four-time world 100m medallist.
With Veronica Campbell-Brown ruled out of the championships because of a doping infringement, Jamaican teammate Shelly-Ann Fraser-Pryce has been left as the country's main contender for gold in the blue riband event.
The double Olympic gold medallist and 2009 world champion, fastest in the world this season with 10.77sec, won her heat easily, taking her foot off the gas for 11.15sec.
Two other Americans, Alexandria Anderson and Octavious Freeman, advanced along with three other Jamaicans including Kerron Stewart, a seven-time medallist in worlds and Olympics including a 4x100m relay gold in Berlin in 2009.
"The final will be quite an open race and this is why I love this sport," said Stewart, who said she had not spoken to double Olympic 200m champion Campbell-Brown since she tested positive.
Nigerian medal hope Blessing Okagbare also won her heat in 11.04sec in her bid to become the first African athlete to medal in the 100m at a world championships.
Also through to fly the European flag were the continent's reigning champion Verena Sailer of Germany, Norway's Ezinne Okparaebo, Briton Asha Philip and Bulgarian Ivet Lalova, while Brazilian duo Ana Claudia Silva and Franciela Krasucki also impressed.
Trinidad and Tobago's Kelly-Ann Baptiste, who took bronze in Daegu two years ago and is third fastest in the year this year, was a notable absentee from the line-ups after reportedly testing positive for drugs.