Onlookers said the Duke of Cambridge got off to a shaky start at the coaching skills session but soon got into the swing of things.
"He came in late, but he adapted very quickly," said Greg Mateo, a mentor helping run the activity at the Westway Sports Centre in Kensington.
"I think we were all confused initially, but part of the objective is to have confusion and work through that confusion and I think he was able to do that pretty well."
The 31-year-old royal then went on to the court to play and delivered some strong serves to his opponents.
However, he was defeated twice by the serve of 13-year-old Vinojh Kalaiselvan.
"Sorry, my bad," the new dad said to his teammates after the first miss.
"I felt a bit sorry for him," Vinojh said. "But it was a very good game, he did well.
"I was nervous playing because I had never met the Prince before.
"I think it was his first time playing, so if he practises and practises, he'll get better."
William's performance was a far cry from his wife Kate's who "picked up the sport really quickly" when she played at the Olympic Park in October.
The sporty Duchess hit the headlines playing in wedges on her first solo engagement since giving birth to Prince George.
William was at the event as patron of The Royal Foundation of The Duke and Duchess of Cambridge and Prince Harry which launched the Coach Core programme in July last year.
The intense programme aims to give 16 to 24-year-olds, often from disadvantaged backgrounds, sports coach qualifications and inspire their peers.
See our photo gallery of William and Kate's best sporting moments