Juan Martin Del Potro brushed aside a code violation issued against him for taking too long between breaks, after marching into the quarter-finals of the Sydney International.

The defending champion, who returned to action on Tuesday following an 11-month lay-off due to wrist surgery, came from a set down to beat top-seeded Italian Fabio Fognini 4-6 6-2 6-2 on Ken Rosewall Arena.

The former world No.4 needed a wildcard to gain entry to the main draw as his world ranking dropped to 338 during his lengthy absence.

But he showed the benefit of concerted preparation by beating Fognini in an hour and 48 minutes on Wednesday.

Former US Open champion Del Potro needed treatment from the courtside trainer during the first set but said there was no major discomfort from his left wrist.

He also said he had no issues with umpire Fergus Murphy who took exception to his slow return to the court from a change of ends and issued a code violation against him.

“It’s my first warning on tour after my surgery,” Del Potro said.

“He’s a good umpire and it doesn’t matter if he called warnings.

“This is my second match on tour after one year. I need to breathe more than the other players.”

Fognini continually targeted Del Potro’s backhand after the Argentine admitted earlier this week he is still managing the pain in his left wrist.

But he grew in confidence and precision as the match progressed, serving 11 aces and winning 80 per cent of points when his first serve was in play.

“My game is to serve strong and try and make winners with my forehand,” he said.

“If my backhand is okay, I will be aggressive with it in the future.

“But now I think I just need to hit the ball as well as I can and don’t try to make winners with my backhand.

“I just need to play a lot of backhands during the point, and if I do that I will get confidence very soon to play aggressive as well.

Second seed David Goffin of Belgium also suffered a second round loss, going down 6-3, 6-3 to Italy’s Simone Bolelli.

Poland’s Jerzy Janowicz, who beat Australia’s Nick Kyrgios in a match that finished in the early hours of Wednesday, crashed out to fifth-seeded Argentine Leonardo Mayer.

Janowicz had a running battle with umpire Ali Nili, who issued violations against him for smashing the ball out of the court in frustration and then taking too long to return after a change of ends.