British pair Perri Shakes-Drayton and Eilidh Child were overwhelmed as Zuzana Hejnova strolled to world 400m hurdles gold in a world leading time in Moscow.

The Czech Olympic bronze medallist trailed American pair Dalilah Muhammad and Lashinda Demus, who claimed silver and bronze respectively, going into the home straight and cruised to the line in 52.83 seconds.

Child competed an impressive 2013 with a fifth place finish from lane eight while Shakes-Drayton suffered knee problems from the outset and hit two hurdles on her way to finishing seventh.

"In the race it felt like my knee was wobbling or doing something that it shouldn't have been doing and that has to be seen to now," the 24 year old told BBC Sport. "I'm gutted obviously I was doing so well and I felt so good but in that race it went rubbish.

"It started before (I hit the hurdle) I wasn't sure what was going on and I was saying 'please hold on' because I was still pushing and then I was losing control. I don't know what's wrong with it."

The commonwealth silver medallist from the Commonwealth Games Child crowned a season where she has progressed throughout by finishing fifth but the Scot was left wondering whether a medal was within reach.

"It wasn't a great race I lost my stride on the back straight and I was just trying to fight back the whole way around and I did feel a bit tired tonight," Child said.

"I can't really complain, fifth in a world final. I wanted to come here and get in the final and I wanted do a little bit better when I was actually in the race.

"It's been the pinnacle (of my season). The whole aim of it was to come here and to make the final and if you said to me I'd be fifth in the world championships I would have taken that.

"Seeing the times I thought I could have run quicker than that and I could have been in contention for a medal and I'm a little bit disappointed about that."

Elsewhere, Britain's Robbie Grabarz crashed out of the high-jump final early on as Ukraine's Bohdan Bondarenko claimed gold.