Ristananna Tracey of Jamaica takes the first heat with a time of 54.88.

The much hyped 17-year-old American Sydney McLaughlin was unable to keep up with the pace in this heat and finished fifth, but watch the name, she still has many years to come.

So, the Netherlands resisted a late Argentine fightback to win 3-2 and set up a semi-final match against Germany.

Great Britain play New Zealand in the other semi.

Steve Cram
BBC athletics commentator on BBC TV

Well that wasn’t very good, was it?

A really slow heat is won easily by Joanna Linkiewicz of Poland, with Janieve Russell also through easily enough.

Janieve Russell of Jamaica goes in this next heat. She has run 53.96 this year but she is struggling with a foot injury.

Let's see...

Colin Jackson
Two-time world 110m hurdles champion on BBC TV

We have been asking a lot of the 17-year-old Sydney McLaughlin. Just getting here was a huge achievement. 

You’ve got to get used to this stage, and that comes with maturity. 

There’s no doubt she’d have learnt so much from this.

Steve Backley
Four-time European javelin champion on BBC TV

That was a high tariff dive...

Wet! The pole vault competition is back under way. They've cleared the runway but a side-effect of that horrendous early rain is that the crash mat is saturated! 

The first man over comes back to his feet absolutely drenched... 

Hold on a minute - what's this?

The Netherlands were 3-0 up in their women's quarter-final but it is now 3-2 with four minutes left....

Two-time rowing Olympic gold medallist Helen Glover is loving her time in the Olympic Stadium.

Ristananna Tracey wins the first heat for Jamaica, as 17-year-old American Sydney McLaughlin ties up badly and misses out on a place in the semis. 

Tom Fordyce
Chief sports writer in Rio

The rain has moved on from this part of Rio for now, with the pole vaulters back out and the discus resumed. Good qualifications on a drying track too for Andrew Pozzi and Lawrence Clark, two more trained in the peerless stable of hurdling guru Malcolm Arnold.

Sandra Perkovic and Denia Caballero have both now qualified for the discus final after a shaky start.

Jonathan Chase: Single false starts are indeed harsh, but does anyone really miss the endless resets that we used to have in the sprints?

Dalton Andrade Filho: Disqualifying a runner after ONE false start is absolutely ridiculous!!! Years of preparation thrown out! IOC, change back to two!

Sort Sport: False starters face a worse punishment than drug cheats.

Lawrence Clark clocks 13.55 and finishes third in his heat to join Andrew Pozzi in the semi-finals

The women's 400m hurdles heats were due to start now but we are of course running late after that poor weather.

GB's Eilidh Doyle in in the sixth heat. She has the sixth best time in the wold this year. 

Image source, Eilidh Doyle

Lawrence Clarke came fourth in the final at London 2012, and tells BBC Sport that he has been waiting for four years to perform on the Olympic stage once more.

"I got out remarkably well, I didn’t want to take any risks, the first round has to be clean, you can’t make any mistakes," he said.

"Tomorrow night I’m coming back with my game face on, it’s a do-or-die race.

"In 2012 I was ranked 26th in the world coming in and finished fourth in the final. I think I’m ranked 31st this year.

"I love it, I’ve been waiting for four years for this."

Through the damp, puddles and a heavy hurdle GB's Andrew Pozzi keeps his composure to qualify in second with a time of 13.50s.

Also, if you want to see true dedication, watch Brazilian's Joao de Oliveira's superman dive over the finish line to qualify in style.

Justin Gatlin is getting booed again as Seb Coe prepares to give out the medals for the men's 100m final.

Usain Bolt looks far from impressed with the reaction inside the stadium.