Pistorius didn't do as he was told. Instead he broke down, and court had to be adjourned for almost an hour.
Shocking though it was, to those in the know it came as no surprise. For one thing, the early part of the trial was the setting out of the state's case, in which Nel wasn't cross-examining anyone. But the reputation of South Africa's "pit bull" prosecutor extends far beyond the country's legal circles. Even the waiters and waitresses in the cafes around Pretoria's legal centre are aware of it. "Everyone thinks he's this nice, gentle guy," one told me. "Just you watch. He isn't."
Some have questioned whether his ferocious opening, in which he nearly bellowed at a sobbing Pistorius of how "Reeva's head exploded like a melon", went too far. What did he establish? What were his tactics? To traumatise and rattle the witness before beginning the crucial task of picking apart his story? If so, so traumatised was he that an hour's break was necessary for him to gather himself.
Watch: Pistorius apologises to Steenkamp family
Should Nel win this case, it will arguably not be his greatest triumph. He has been well known in South Africa since he ripped apart the corrupt former police commissioner Jackie Selebi in the witness box.
In that case, a huge police party had raided Nel's home in the early hours and arrested and charged him. He was unshaken.
Of course, it is likely that most of those who've been shocked and appalled by his somewhat brutal manner have never seen a real life murder trial before. They are not televised in Britain, and in South Africa this is a first. The state's position is that Oscar Pistorius killed Steenkamp intentionally and his story is a fabric of convenient and calculated lies. If it is, it is Nel's job to rip it apart. If it is robust, of course, he won't be able to.
Watch: Pistorius describes moment girlfriend was killed
Several times on Thursday, Nel brazenly put it to Pistorius: "You are lying."
The athlete maintains he wasn't.
Weeks ago, police ballistics expert Captain Chris Mangena told the court that a Glock gun that was accidentally discharged in a Johannesburg restaurant is a type that is "impossible to discharge without pulling the trigger".
Pistorius was holding the gun at the time, but insists he didn't pull it.
"A miracle," Nel called it.
"I put it to you, there is no other way that gun could have gone off than you pulling the trigger. You are lying."
Only Pistorius knows for certain what happened in his house that night.
"The only other witness is dead. You killed her," Nel has reminded him many, many times.
The devil will be in the detail, which is currently under examination. Pistorius says he ran on to the balcony and screamed for help, and yet when the police arrived to take photographs, a large tripod fan was blocking the way. It was apparently pitch black, but he saw Reeva's legs under the duvet as he got up. A plug extension cord that doesn't seem to stretch far enough to where Pistorius maintains it must have been.
There is no, real, concrete proof for Nel to go on, and he must prove beyond reasonable doubt that Pistorius knew who was behind his toilet door when he fired four bullets through it. It's a difficult job - perhaps impossible. But there is no one better around to do it.
• With more than 30 years' experience, Nel is one of South Africa's most respected legal minds and is widely praised for his meticulous attention to detail.
• He is known for his no-nonsense attitude inside the courtroom which has earned him the nickname the Pit Bull and has racked up a string of successful prosecutions.
• He has built his reputation around high-profile cases he prosecuted on corruption charges former police boss and Interpol's ex-head Jackie Selebi, whom he called an "arrogant liar'' during cross-examination.
• He was the founding head in 1999 of the Gauteng province division of South Africa's elite police and prosecution unit the Hawks, then known as the Scorpions.
- Independent
