Rafael Nadal is back in form on the tennis court – and in his sharp-tongued critiques of the ATP tour.

The second-seeded Spaniard reached his first quarter-final since capturing his record ninth French Open title in June with a 6-3 6-4 win over German qualifier Peter Gojowczyk at the China Open on Thursday, then blasted the choice of tennis balls at the tournament.

“The ball is so bad here,” Nadal said.

“If you throw the ball on the floor, the bounce goes everywhere. Is not a question of winning or losing. I won in Rio (earlier this year) with this ball. I won tournaments with this ball.

“It’s just that we’re competing at the top level of our sport, tennis, and the ball is an important thing.”

The 14-time major winner has complained previously about the ball in question – manufactured by Head – but he also criticised the decision to switch ball manufacturers from tournament to tournament, saying it could result in injuries.

“This week we are playing with one ball. Next week we are playing with a different ball,” he said. “That’s dangerous for the shoulder, dangerous for the elbow.”

The Spaniard wasn’t nearly as critical of his own game in his second match back from a two-month layoff due to a right wrist injury.

He was sharp for much of the match until the final game when he double-faulted and made two unforced errors to give Gojowczyk three break points. He fought them off, however, and closed it out on his fourth match point.

Nadal faces another qualifier in the quarter-finals, Martin Klizan, who advanced when seventh-seeded Ernests Gulbis of Latvia retired with a shoulder injury while trailing 6-2 3-0.