After passing the last vehicle, Welsford pulled into the left lane and both cars accelerated heavily, driving side by side and reaching speeds up to 183km/h.
Spoken to a short distance away, Welsford described what he had done as "being stupid, I guess. He came up beside me and we just went for it".
Counsel Andy Belcher said the speed alleged was 183km/h.
There was some discussion between the officer and the defendant as to his speed being 141km/h, not 183km/h, "a reasonably material difference ... but he wants to get on and get it dealt with today".
"The other driver just put his foot down and sped off," Belcher said.
Welsford was warned for the lockdown breach, police prosecutor Tim Hambleton said in response to a question from Judge Michael Turner.
Welsford told the judge he had been dropping the car off at his brother's place.
"What was going on in your mind?" the judge asked.
"I wasn't thinking straight," Welsford replied.
He had not previously appeared before the court.