Harry got up and threw the knife at him and at the same time muttered the Gemino curse which duplicated the flying knife and followed it up with two quick 'Reductos. WHile he aimed one directly at Voldemort, the other he shot st the Dark Lord's feet.
Voldemort who was about to casually deflect the first knife was suddenly put on the defensive as the rushing knife mutliplied into two and then there wenre those two curses. He had to change his plan halfway through the incantation for banishing the rushing knife away and instead form a shield which would protect him from both the knives as well as the curse aimed at him.
Harry having already predicted this outcome simply moved to the side to avoid the deflected REductor curse. The other curse's aim was true though and it served its purpose. The Reductor curse blew up the ground at Voldemort's feet kicking up pebbles and dust blinding the Dark Lord.
The Death Eaters, in the meanwhile, had not tried to do anything to help their Master as they knew that interfering in a duel initiated by the Dark Lord would result in punishment. Their Master was as cruel with his followers as with his enemies.
After Harry dodged the returning curse, he whirled around and whispered 'Defodio' thrice. This spell which he had discovered in the course of reading about dragons was meant for blasting walls and which one wizard had tried to use against a Chinese Fireball. This time he aimed the curse near the feet of the Death Eaters in three directions. It worked with great success. These curses, obviously being immensely powerful compared to the Reductor curses blasted huge craters where it hit the ground kicking up so many rocks and dust. A few unwary Death Eaters were blasted off their feet with the force of the explosion. The shrapnel of blasted stones injured those few who weren't quick enough to shield themselves magically. Still, the explosions and the dust disoriented and blinded all of them. The massive amount of dust kicked up by the multiple blasts created an ideal smoke-screen and a smoke-screen was what Harry needed in order to make his escape. He crouched and started stealthily making his way away. He came across a couple of Death Eaters who were dazed from the blast. They started to raise their wand but Harry had already cast two muttered Severing Curses at their torsos slashing viciously twice in the air. Since the Severing Curses did not emit a flash of light or any sound, the Death Eaters at first though that Harry's curses had failed. Their sneers were cut short when they felt as if someone had cut them with a knife. They stopped mid-incantation to look down and found a deep gash in their stomachs. That was all the chance Harry needed in which he cast a Body Bind Curse aimed at both together. Their hands and legs snapped together and they fell down with a thud.
Harry again started to make his way, taking care to use a circuitous route, towards where Cedric's body lay. He had worked out that the same Cup which brought him here could take him and Cedric's body back. He would not leave Cedric's dead body behind.