Melbourne - The Australian Open's new balls this year are dividing opinion at Melbourne Park, with even the two greatest men's Grand Slam winners of all-time failing to see eye-to-eye.
Roger Federer, winner of 20 Slams, says the new Japanese-made Dunlop balls behave differently in cooler night conditions and do not allow players to "out-spin" rivals.
But Rafael Nadal, the 17-time major winner renowned for his huge top-spin groundstrokes, countered: "I can't say it's a bad ball."
Australian John Millman reckoned "they're a bit heavy" after losing on Wednesday night while his big-mouth countryman Bernard Tomic pulled no punches, saying they were "dead" and "really shit" before he lost in the first round.
Tournament director Craig Tiley has defended the change from Wilson balls, claiming earlier in the week he had heard only "positive feedback".
He might have to change his mind after defending champion Federer offered a different opinion on Wednesday.
"Well, they definitely play a touch different to the ones we've had the last couple years," said the Swiss master, who is going for a third consecutive title and record seventh in all at Melbourne Park.
"At night the spin is not taking off tremendously," he added, noting that the semi-finals and final are played at night.
"It's hard to out-spin guys here. I just feel like it's really important to have fast enough courts for night session conditions. If you keep it slow, slow, at night the ball doesn't move."
Nadal, who is bidding to become the first man in the Open era to win each Grand Slam on two or more occasions, acknowledged the ball was different but reckons it is "fair for everyone".
"The ball is big. With colder conditions, especially during the night, the ball is bigger," said the Spaniard, who won his lone Australian Open title in 2009.
"Yes, the ball is going a little bit more slow, no? Not the high bounces that sometimes we used to have here. But the ball is what there is. It is fair enough, a good quality ball. I can't complain."
Federer was characteristically diplomatic with his criticism. "Look, one year ago it was too far back. Honestly it's still early in the tournament to exactly tell you how it feels exactly," said the maestro.
"I definitely have to go through a minor adjustment maybe from Perth, which was a faster court.
"I still feel like you can serve your way out of trouble. It is true, you can't out-spin a guy here. I think that's clear."
But it was Millman who probably summed up the locker-room feeling best of all: "Some people love 'em, some people don't."