Chris Brown of the Bahamas and Kirani James of Grenada lead the pack during the Men's 400m semifinal on Day 9 of the London 2012 Olympic Games on 5 August 2012 (Getty Images) © Copyright
The men's 400m flat saw the defending champion and world leader LaShawn Merritt pull up in the heats to throw the contest wide open, then both his US team-mates Tony McQuay and Bryshon Nellum also failed to make the final.
Kirani James is the reigning World champion and looked good in the semi-finals with 44.59. Trinidad & Tobago's Lalonde Gordon impressed with a big PB of 44.58, while the Borlee brothers Jonathan and Kevin also made it through. Also watch out for teenager Luguelin Santos who has been running well all year with a string of sub-45 clockings.
The men's 400m Hurdles also looks set to be a far more open affair than it initially seemed. Expected to be a two-horse race between World champion Dai Greene and world leader Javier Culson, the Briton only scraped through to the final as a fastest loser while 2004 Olympic champion Felix Sanchez tore up the form book with a world-leading 47.76 in the semi-finals.
Culson qualified comfortably, but Jehue Gordon and defending champion Angelo Taylor also dipped under 48 seconds to put themselves in contention for a medal. Taylor's US team-mates Kerron Clement and Michael Tinsley will also be in the final, and it's not beyond the realm of possibility that either of those could sneak a top-three spot too.
The other track final of the evening session is the women's 3000m Steeplechase, and the top four from last year's World Championships will once again clash. World champion Yuliya Zaripova is the marginal favourite, and she showed in Daegu last year that she has a devastating finish.
On that occasion, Milcah Chemos was tipped to win gold but the Kenyan wound up third. She will want to go at least one better than that, and she comes to London in good form too, having broken the African record earlier this year.
Ethiopia – the only nation with three athletes in the final – will also be strong and they are led by national record-holder Sofia Assefa. Defending Olympic Champion Gulnara Galkina also made it through to the final, but she is not in the same form that saw her become the first and only woman to break nine minutes.
Isinbayeva out to regain crown as the queen of pole vaulting
In recent years Yelena Isinbayeva's aura of invincibility has taken a bit of a bashing. After a break from competition in 2010 she has returned in good form, setting a World indoor record of 5.01m and taking the World Indoor title.
She no-heighted in her last competition before the Olympics, but looked good in qualifying as she popped over 4.50m and 4.55m with ease. Her challenge has also been made easier by the fact that World champion Fabiana Murer and former World record-holder Svetlana Feofanova failed to make the final.
But last year's World Championships showed that Isinbayeva is beatable, and her main rivals Silke Spiegelburg and Jenn Suhr will go into tomorrow's final full of confidence.
The other final due to take place tomorrow is the women's Shot Put, following the qualifying round in the morning session. Nadezhda Ostapchuk has been in superb form this year and owns the top three marks of the season, but can she carry that form outside of Belarus?
An even bigger question is whether she can defeat reigning champion Valerie Adams. The New Zealander is undefeated since 2010 and has also been in the form of her life, producing three of her five best career marks this season and winning World Indoor gold in March.
Fraser-Pryce begins campaign for second medal
Having won the 100m gold on Saturday, Jamaica's Shelly-Ann Fraser-Pryce will be back on track tomorrow evening in the 200m heats as she looks to win another medal.
But Allyson Felix, who has taken silver in this event at the past two Games, is desperate to win her first individual Olympic gold. Carmelita Jeter and Veronica Campbell-Brown, the silver and bronze medallists in the 100m, will also be doubling up.
The semi-finals of the women's 400m Hurdles also takes place tomorrow evening and they look to be highly competitive. Natalya Antyukh faces Zuzana Hejnova in the first semi, with LaShinda Demus taking on Perri Shakes-Drayton and Kaliese Spencer in the second. Melaine Walker perhaps has the easiest semi-final in the third race as she's up against Denisa Rosolova and Georganne Moline.
There's another packed session in the morning at the Olympic Stadium as World champion Sally Pearson will be looking for a good start in the women's 100m Hurdles heats, David Rudisha will highlight the men's 800m heats, and exciting clashes are expected in the women's 1500m heats. The men's Discus Throw qualification rounds will also take place.
Jon Mulkeen for the IAAF
- Chris Brown of the Bahamas and Kirani James of Grenada lead the pack during the Men's 400m semifinal on Day 9 of the London 2012 Olympic Games on 5 August 2012 (Getty Images) © Copyright
- Felix Sanchez of Dominican Republic celebrates after competing in the Men's 400m Hurdles Semi Final on Day 8 of the London 2012 Olympic Games at Olympic Stadium on August 4 2012 (Getty Images) © Copyright
- (L-R) Sofia Assefa of Ethiopia and Emma Coburn of the United States competes in the Women's 3000m Steeplechase Round 1 Heatson Day 8 of the London 2012 Olympic Games on 4 August 2012 (Getty Images) © Copyright
- Yelena Isinbayeva of Russia competes in the Women's Pole Vault qualification on Day 8 of the London 2012 Olympic Games at Olympic Stadium on August 4, 2012 (Getty Images) © Copyright
- Valerie Adams ready to unleash her 20.60m winning heave in New York (Victah Sailer) © Copyright
2005 Gatlin wins in Daegu
2000 Women's Marathon