The double amputee will get a chance to run for an Olympic medal after track officials awarded an extra spot in the final following a successful protest by South Africa.
In the opening round Thursday, a Kenyan runner collided with South Africa's Ofentse Mogawane as he made his way around the final bend in the second leg of the race. Mogawane fell and clutched at his left shoulder as the baton rolled away.
Set to run next in the relay, Pistorius stared at the scene in disbelief. He put his hands on his head and began walking off the track, figuring his time in London was done.
In the span of two hours, Pistorius went from crestfallen to celebration. On Twitter, he said, "IT'S ON!! We in the FINAL."
Following the race, Kenya was disqualified from the competition when the referee ruled that Vincent Mumo Kiilu cut across too soon and caused Mogawane to fall. Kiilu had a spike mark on the back of his right shoe and Mogawane dislocated his shoulder.
Track and field's governing body said Pistorius' team will run in an outside lane after the jury met and "agreed to advance the South African team, even though they did not finish the race, considering that they had been severely damaged in the incident with Kenya."
Originally, three teams from the two heats were supposed to advance automatically, along with the next two fastest times. The last lane was going to be empty. The Bahamas, the U.S., Britain and Trinidad and Tobago were among the other qualifiers.
Willem Coertzen was competing in the decathlon and glanced up after Mogawane hit the track, but wasn't aware of South Africa's inclusion in the relay final until after he'd finished pole vault.
"I'm ecstatic," said Coertzen, who is South African. "I haven't seen it happen before like that, could be something new, but I'm excited for them. After everything that (Pistorius) has been through, good luck to him."
This was quite a day for Pistorius.
Quite an Olympics, too.
After a long battle for inclusion in able-bodied competition in the individual events, Pistorius ran the 400 meters and advanced to the semifinals before finishing last in his heat.
Last week, the IAAF announced he could run any part of the 4x400 relay at the Olympics, not just the opening leg when runners have to remain in their assigned lanes for a lap.
"This whole experience was one of the highlights of my career," said Pistorius, the first amputee to compete in track at the Olympics. "I just had the most amazing experience representing my country. My experience here, everything has been superb. From the organization to the crowd to the fans and to friends. I couldn't have hoped for a better time.
"It's so hard. You have so much support from back home. We would have loved to have represented our country today and finished the race."
Now, as it turns out, Pistorius and his teammates will get that chance.
"Will be up on the 3rd leg tomorrow for the Final! Really can't wait!" he posted on Twitter, adding "Emotional roller coaster!"