GB duo Ohuruogu and Idowu off form ahead of Worlds
Britain's top medal hopes suffered a disappointing day in their final major event before the World Championships in South Korea.
Olympic 400m champion Christine Ohuruogu finished last in her event in 51.87 seconds at the London Grand Prix.
And triple jump world champion Phillips Idowu placed third with a best effort of 17.07m.
"I don't know what happened, to be honest - I felt really good, and I warmed up OK," Ohuruogu said.
"I had a cold last week but it's gone now. I'm very shocked.
"My coach [Lloyd Cowan] is going to tell me that that was rubbish, and he'll be right."
Idowu also disappointed in the triple jump, finishing behind 21-year-old American Christian Taylor and Nigeria's former Briton Tosin Oke.
Idowu - who pulled out of the British trials last weekend - blamed his poor form on the extra workload of his training, but was in downbeat mood after failing to impress in front of his home crowd.
"It's not the performance I wanted - I wanted a decent jump before Daegu," he told BBC Sport.
"I have been doing a lot of heavy work and I just didn't have it in the legs - I worked really hard but I didn't quite have it.
"I made the decision not to compete last weekend because I knew I wasn't quite right. I had hoped that I'd had enough time to recover but this was exactly what I didn't want.
"Usually most years at the major championships I am able to turn it around.
"With Teddy Tamgho not competing at the Worlds I'm actually working harder in training than I usually would at this time of year to get the preparation right, but it is affecting my competitions."
Ohuruogu missed both the Europeans and the chance to defend her Commonwealth title last year after a tear of the quadriceps.
She spent the winter training in Jamaica but struggled again at the start of this year and has been left desperately short of training time and racing form.
She said: "My instruction was to hit it hard over the first 200m but then felt Rosemarie Whyte just flash past me, and I thought - am I really going that slowly?
"I tried to pick it up but it just wasn't there. I have to be realistic - I've not done as much training and I'm trying to catch up. I'm fortunate to have the qualifying time already but there is a lot of work to be done.
"We've had a total of five 400m sessions this year so it's a case of putting work back in tank, but I'm really, really behind. I don't want to go to Daegu in a hot mess. We'll have to see where we can sharpen up in the time we have."
Richards-Ross is coming back from her own injury problems this year, and afterwards backed her old rival and friend.
"Christine has shown that she is excellent at championship meets," said Richards-Ross. "Like me she has great experience so I think she'll definitely be one of my top competitors."
But BBC Sport analysts Denise Lewis and Colin Jackson questioned whether Ohuruogu should forget about her World Championships ambitions this year and try to get in shape instead to defend her Olympic title next summer.
"That was a terrible race for her," said Lewis, Olympic heptathlon gold medallist in 2000.
"It's soul-destroying watching her race just fall apart. It's hard to be a world and Olympic champion looking like a shadow of yourself, and it's a question of whether she should be going to Daegu."
Jackson added: "The team will say, 'We're not in the shape we want to be, so we may leave the World Championships this time - try to concentrate on getting well and keeping fit so you can work day in, day out."