Sprinters such as Justin Gatlin, Tyson Gay, Walter Dix and LaShawn Merritt are all under heavy pressure.

The US trials system which sees the first three home being selected - subject to meeting qualification times or distances - always makes for drama, and there will be plenty more over the course of the weekend with the arrival of startling new talents such as Christian Coleman, who has just turned professional after setting a 100 metres time of 9.82sec on June 7.

That is the fastest so far this year while Fred Kerley last month ran the fastest 400m time seen this year, 43.70, at an National Collegiate Athletic Association qualifying event.

The 23 Olympic champions include Allyson Felix, Gatlin, Brittney Reese, Christian Taylor, Matt Centrowitz, Michelle Carter, Ryan Crouser and Stephanie Brown Trafton.

In addition to the top three, reigning world champions from 2015 and Diamond League champions from 2016 receive automatic byes into the London World Championships that run from August 4 to 13, assuming they compete in Sacramento.

Tomorrow sees the opening heats of the men's 100m – which may lack any of the top three US finishers at the Rio Olympics. 

Olympic silver medallist Gatlin has yet to break 10 seconds this year, Trayvon Bromell, who was eighth, has not raced since Rio following Achilles tendon surgery and 15th-placed Marvin Bracy is also recovering from surgery.

Meanwhile six US men under 23 have broken 10 seconds this season, with Coleman heading the list, followed by Cameron Burrell, the son of former world record holder Leroy, and Ronnie Baker, who beat Olympic silver and bronze medallists Gatlin and Canada’s Andre De Grasse to win at last month’s IAAF Diamond League meeting in Eugene.

The story looks potentially the same in the men's 200m, where Coleman and Noah Lyles - who won the IAAF Diamond League in Shanghai in 19.90 - are the only two Americans under 20 seconds this season, with Chris Belcher at 20.01. 

None of them have raced individually at an Olympics or worlds, but they appear ready to step up.

Olympic 1,500m champion Matt Centrowitz is favourite, but he will be challenged by Olympic 800m bronze medallist Clayton Murphy, who is seeking an 800/1,500m double.

Ajee Wilson is back to racing after the US Anti-Doping Agency announced that she would lose her indoor national 800m record of 1:58.27 on February 11 - after her sample showed up positive for the anabolic agent zeranol – but received no ban after it was concluded she had eaten US meat, which contains this agent.

She looks a strong hope in the 800m, although she may be race-rusty, and will face opposition from in-form 2013 world medallist Brenda Martinez and Raevyn Rogers.

The women's 1,500m will feature the third and fourth-placed runners from Rio 2016, Jenny Simpson and Shannon Rowbury, plus Rio Olympic 800m finalist Kate Grace.

Much media coverage will be accorded to Gabriele Grunewald, who is racing while having ongoing cancer treatment.

In the men’s 3000m steeplechase, Evan Jager is looking for his sixth straight US title, while Galen Rupp will be going after a ninth consecutive win in the men’s 10,000m in what could be his last track race on US soil.