Nick Kyrgios lets his racket do the talking as Aussie knocks out Stan Wawrinka at Madrid Open

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Australian Nick Kyrgios knocked fourth seed Stan Wawrinka out of the Madrid Open with a scintillating display on Wednesday.

Last year the 20-year-old got a suspended 28-day ban and $25,000 fine after making lurid remarks about Swiss Wawrinka's girlfriend during their match at the Rogers Cup in Montreal.

Kyrgios, who has had several brushes with authority, was widely criticised, but his 7-6(7), 7-6(2) second round victory on Wednesday was further proof of a growing maturity after he won his first ATP title earlier this year in Marseille.

Nick Kyrgios celebrates as he knocks out reigning Roland Garros champion Stan Wawrinka in Madrid

Kyrgios (right) and Wawrinka shake hands after Wednesday afternoon's match at the Caja Magica

Wawrinka's girlfriend Donna Vekic, of Croatia, watches the match from the stands in Madrid

Vekic was the subject of lurid remarks by Kyrgios during his match against Wawrinka in Montreal last year

There was the odd outburst at the umpire, one after a first serve during the first-set tiebreak was called out despite appearing to clip the line, but Kyrgios kept his emotions in check to edge a tight tussle.

Japan's Kei Nishikori, the sixth seed, had a narrow escape before joining Kyrgios in the third round.

Italy's Fabio Fognini recovered from losing the opening set to level the match and served for the match at 5-4 in the decider before imploding.

Nishikori won 6-2, 3-6, 7-5 to set up a meeting with Frenchman Richard Gasquet. 

Kyrgios (right) looks at a ball mark on the red clay with umpire Mohamed Lahyani during the match

Kyrgios argues with umpire Lahyani about the mark but brushed it off to later secure victory

Kyrgios plays a forehand during his straight-sets victory in the second round of the Madrid Open

Wawrinka (top) looks to play a forehand past Aussie Kyrgios, who stands at the net in anticipation