Melbourne: A new format called Fast4, which some have dubbed disco tennis, was again on display Wednesday with a recovering Rafael Nadal happy to be on the dance floor. The occasion was the official opening of the newly renovated Margaret Court Arena that will give the Australian Open, which starts on Monday, its third stadium with a retractable roof.

On Wednesday, 7,500 fans crammed into the arena for a benefit night for the Rafa Nadal Foundation, which assists socially disadvantaged youth.

It also showcased the Australian-developed Fast4, which features major rule variations to speed up the action for players and fans - no advantage scoring, lets are played, and the first to win four games wins the set.

Nadal's 4-1 first-set win against an Australian junior lasted only 17 minutes.

The often no-nonsense Nadal, introduced to the crowd through a haze of dry-ice smoke and loud music, clearly enjoyed the new format. He joked with the spectators on numerous occasions and once playfully hit a ball into the crowd when someone interrupted him during a serve.

He later took a few "selfies" with his mobile phone.

Earlier Wednesday, Nadal had a training session at Melbourne Park, indicating he might be overcoming some recent health and injury issues.

Nadal was sidelined for three months with a right wrist injury after Wimbledon. He briefly returned in Beijing in late September, advancing to the quarterfinals.

He then had appendix surgery in early November, which he is still recovering from, saying last week in Qatar that he was far from 100 percent.

"This is the third comeback of my career after injury, so we will see how it goes," Nadal said.

On Wednesday night, he also played a set against former Australian player Mark Philippoussis, winning 4-1 in 15 minutes, and a five-setter against Fernando Verdasco, who earlier in the day beat Gilles Simon in straight sets across town at the Kooyong exhibition tournament.

"It was too quick, I feel like I didn't get a chance to take it all in," said the 38-year-old Philippoussis, who now plays senior tennis.

Fast4 matches don't generally last longer than 75 minutes, even at five sets, with each set lasting about 15 minutes. When a set gets to three games all, a five-point tiebreaker is played - and it's first to five, no need to lead by two points to win.

A big departure is the no let rule - serves that hit the net and bounce in the service area on the other side are good. Verdasco mildy complained to the chair umpire after a net cord, asking for the point to be replayed before being reminded of the Fast4 rules.

And at 40-40 and with no deuces, a Power Point is played. The player receiving gets to choose which side of the court the ball is served to.

Also, players are not allowed to sit down during changeovers and play must resume within 60 seconds of the previous game finishing. There is a 90-second break at the end of each set.

Earlier on Monday, the sport had more spectators than the rain-delayed Big Bash League.

The new format is designed by Tennis Australia and launched this week with an opening game where Roger Federer got the better of Lleyton Hewitt in five sets.