Kristina Vogel and Elis Ligtlee also rack up straight-race wins to join Britons Becky James and Katy Marchant in the semi-finals.

That is a bronze medal at least assured for Great Britain at the event.

I suspect that James and Marchant will be aiming a little higher.

Laura Trott in the omnium time trial next.

Adrian Moorhouse
1988 Olympic 100m breaststroke champion on BBC TV

What a brilliant, brilliant, finish.

Spiros Gianniotis of Greece had been given the win in the men's 10km open water race but the decision has now gone to a photo finish.

In a dramatic finish, Great Britain's Jack Burnell may have got bronze.

Adrian Moorhouse
1988 Olympic 100m breaststroke champion on BBC TV

This is going to be a photo finish. 

They are all looking very strong.

The Olympics are over for Britain's Charlie Grice after he was bumped and faltered badly in the closing stages of the men's 1500m heats.

Grice was in position to qualify with 50m to go but eventually finished 11th after running three minutes 48.51 seconds.

BBC Sport commentator Brendan Foster said Grice "promised so much but delivered so little".

Ouch.

The good news is that fellow Brit Chris O'Hare finished fourth in heat one to reach the semi-finals.

Adrian Moorhouse
1988 Olympic 100m breaststroke champion on BBC TV

This is a heavyweight battle. Jack Burnell is on the back of Tunisia's Oussama Mellouli and has looked very comfortable. I think he has got something left in him.

Aimee Lewis
BBC Sport in Rio

"Ladies and gentlemen, please don't go too close to the railings, these riders reach speeds of 70kph," says one of the stadium announcers. Sometimes, as we've seen this week, cyclists also ride on the railings. 

No such shenanigans today, though. British duo Becky James, the 2013 world champion, and Katy Marchant progress to the semi-finals of the cat-and-mouse sprint so it's a successful first session at the velodrome. 

Image source, .

Katy Marchant joins Becky James in the sprint semi-finals - following her team-mate's lead with a straight-races win.

She has absolutely trounced the Lithuanian Simona Krupeckaite over those two races.

Emphatic.

Alistair Magowan
BBC Sport in Rio

Image source, BBC Sport

Plenty of international support as the crowds flock around the big screen to watch the climax of the men's marathon swimming.

Tom from the United States says this is the 20th different sport he's seen in Rio. "I thought I might be able to see a bit more," he says as he gazes out to sea. "But I'd rather be amongst the fans and outside than watching on TV."

There's a contingent of Aussie fans looking tense as  countryman Jarrod Poort is overtaken in the lead. The epic-sounding music they play as events near their finish is not helping their nerves either.

Image source, BBC Sport

Usain runs in the 200m heats at 16:46...

Becky James grits it out, getting the hammer down along the home straight and holding off Zhong Tianshi's challenge by half a wheel.

She will not have to have a third ride-off and is in with a good shot of a second medal of the Games.

Becky James comes into the second heat, leading Zhong Tianshi of China 1-0 after the first race.

She will set the pace in the second heat.

Keep it simple stupid.

Great Britain's Jason Kenny goes from the front and has the pace to take the other six riders out of the equation.

Fabian Puerta of Colombia joins him in the second round. 

The rest are into a repechage.

Now back for the second heats in the women's sprint first round...

Aimee Lewis
BBC Sport in Rio

The track centre is much like a pre-parade ring. These cycling thoroughbreds are slowly circling around the podium, warming up, warming down, giving us a glimpse of what's to come. The guitar riff of Black Betty is bellowing out of the sound system. Oh, it's all too dramatic for me. 

Image source, .

Three rounds in and American Christian Taylor remains in the lead in the men's triple jump final, thanks to his first-round leap of 17.86m.

USA's Will Claye and China's Bin Dong are still second and third respectively.