Veteran yet versatile track stars Veronica Campbell-Brown of Jamaica and American Allyson Felix open up their Olympic campaigns in the hotly-anticipated women's 100m on Friday.
Heats for the blue riband event get under way in the morning session, with the semi-finals and final scheduled for Saturday's evening session at the Olympic Stadium.
The event is sure to be a tester for the two sprinters who have dominated the 200m for the past several years.
Campbell-Brown is the defending 200m Olympic champion and current world champion, while Felix is a former three-time world champion.
While not outright favourites, the duo's long-term rivalry will surely light up the stage of the 100m, in which defending Olympic champion Shelly Ann-Fraser of Jamaica and in-form American world champion Carmelita Jeter also compete.
"I'll take it step by step, day by day and round by round," said the 30-year-old Campbell-Brown, playing down a couple of blips in her build-up to the London Games.
"I've trained hard this season. I'm not going to let losing a couple of races deter my confidence.
"I was maybe a little tired at the trials, but I got into the team, so mission accomplished.
"It's my fourth Olympic Games and I'm excited to be running the two races. In Beijing it was only the 200m. I'll do my best, as usual."
Campbell-Brown added: "The biggest part of performing well is mental preparation. I try not to get too distracted and focus on what I have to do.
"There's a huge mental focus. It all comes down to execution. I will give my all and see what happens.
"The US and Jamaica have been going back and forth over the years in the sprints. I do enjoy running against each other. I do enjoy the rivalry, it's great for the sport.
"Allyson and I do speak but don't hang out. We've been competing against each other for several years. I've been in good shape at Olympics and she won the worlds before I won last year."
Felix admitted that she was a rank outsider for the 100m, but said it was a very handy boost towards reclaiming dominance in the 200m, having ceded her world crown in Daegu, South Korea, last year in biddding for an ambitious 200-400m double.
"Last year I ran the 400m and I didn't have my typical burst of speed," she said. "It was a weird feeling to get to a spot and realise I didn't have that extra gear.
"This year the sprints have helped me stay aggressive."
The 26-year-old Felix added: "Even though I think the 100m helps me a lot for my 200m, I'm still very invested in it and I still think I can do really well. I know the odds are definitely against me.
"I've been working so hard and I think I can still get it done. Once that's done, my attention will turn to the 200m."
Tianna Madison is the third American on the roster, but Jeter will likely prove the strongest competition for gold.
"This Olympic experience has been amazing. The 3rd can't come fast enough, I feel like the day before Christmas," tweeted Jeter, who will also be eyeing a sprint double after claiming the 200m silver behind Campbell-Brown in Daegu.
