Sutton (40) is closing in on Lone Pine, having run 196km. The final leg is a 1400m vertical ascent to Whitney Portal and the finish line, now just over 22km from his reach.
"We hit a low point coming down from Cerro Gordo," support runner Scott Wilson said.
"He was on death's door, but then Glenn tapped into a second wind of sorts and the last ten hours have been a pretty amazing feat of human mental and physical endurance.
"He stepped up the pace to Darwin and then kept that momentum all the way back towards Lone Pine, picking off people as he went."
Wilson described this part of the race as "ugly".
"We are at the stage where you take places by people falling apart in front of you," he said.
US runner Harvey Lewis won the race in a time of 23:52.55 with Australian runner Grant Maughan in second in a time of 24:43.08. Portuguese runner Carlos Sa finished third. Alyson Venti, of USA, was the first female to complete the race in a time of 28:37.28.
