The Marathon de Sables entered its longest - and potentially decisive - stage on Wednesday as competitors crossed 75km of burning Sahara desert.
The fourth stage of the 28th edition of the race, will last for at least seven hours for the elite athletes, and up to 30 for those further down the field.
A mass start for the bulk of the field took place at 0830gmt, with the top 50 men and top five women sent off three hours later.
Initially they traversed a small col, crossed the Rhéris wadi again before confronting the large mass of dunes for the first time, which span several kilometres.
After conceding over 30 minutes in the first leg, Jordanian titleholder, Salameh Al Aqra, has been gradually making up his deficit.
At the start of the day he was 'just' 25'39'' shy of the leader Mohamad Ahansal and eight minutes behind Aziz El Akad.
Third on Tuesday, Ahansal has probably managed his race with a view to this major leg, which could see him take his fifth title.
Among the women, Laurence Klein from the Champagne region hasn't given her rivals the slightest sign of hope.
Victorious in the first three legs, she will have to keep her eye on the attack from American Meghan Hicks and Briton Joanna Meek, who are hot on her heels 24 minutes and 28 minutes behind respectively.
"It is going to be a long day so just concentrate on looking after your body for the whole way, eating at the right time, drinking and that, it is nothing," said 13th-placed competitor, Andrew Fargus. "If you go too fast at the beginning you are in trouble."
Thursday is a rest day before Friday's final 42km leg.
Presented by Adam Justice