After a routine Supreme Court argument on Wednesday, Chief Justice John G. Roberts Jr. asked the lawyer who had represented the government to return to the lectern.

“You have just presented your 160th argument before this court, and I understand it is intended to be your last,” the chief justice told the lawyer, Edwin S. Kneedler, who is retiring as a deputy solicitor general. “That is the record for modern times.”

Chief Justice Roberts talked a little more, with affection and high praise, thanking Mr. Kneedler for his “extraordinary care and professionalism.”

Then something remarkable happened. Applause burst out in the courtroom, and that led to a standing ovation for Mr. Kneedler, with the justices joining, too.

“It was a rare moment of unanimity and spontaneous joy from all nine justices on the bench,” said Richard Lazarus, a law professor at Harvard. “They were all beaming.”

Kannon Shanmugam, a veteran Supreme Court lawyer, said it was “one of the most electric moments I’ve ever seen in the courtroom.”