Kyrgios bemused by rare service faults

A repeated foot fault infringement threatened to hammer the nail in Nick Kyrgios' coffin during his fourth round Australian Open clash with Grigor Dimitrov on Sunday night.

The Aussie was already two sets to love down against the Bulgarian 3rd seed when he was pinged with his second foot fault of the night.

"I haven't been called for a foot fault for the last three years," an irritated Kyrgios shot back at the chair umpire.

"That's twice today. It's not possible man."

Replays showed that the Aussie's trailing right foot did arguably stray across the centre of the service square, with commentator Jim Courier conceding he thought the officials got the call right.

Kyrgios was perplexed by the foot fault calls. Pic: Ch7/Getty

In further evidence of the 22-year-old's improved maturity, Kyrgios brushed aside the frustration to hold his serve before breaking Dimitrov as he hung on in the match.

The Aussie's serve continued to cause his rival problems and the 22-year-old made the most of the break to claim the third set 6-4 - keeping his tournament hopes alive.

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Dimitrov had a chance to serve for the match at 5-3 up in the fourth set but Kyrgios broke before taking his next three service games to love - forcing yet another tie-breaker.

However, the Aussie's joy was short-lived as Dimitrov again upped the ante to take the breaker 7-4 and with it, the match.

The Bulgarian next faces Britain's Kyle Edmund in the quarter-finals.

Dimitrov's serve was on song from the outset with Kyrgios unable to break it in a pulsating opening set that was destined to go into a tie-breaker.

Dimitrov grabbed a crucial mini break early on the tie-breaker and never relinquished his advantage as he saw it out 7-3 to claim the opening set.

The second followed in a similar vein until the first real moment of controversy reared its head.

Dimitrov's coach appeared to question whether Kyrgios' team were giving him illegal instructions from the player's box, clearly unhappy as he gestured towards the chair umpire.

Kyrgios could be heard talking to his team throughout the match but there was no suggestion he was receiving illegal advice back from them.

Lleyton Hewitt suggested in commentary that it could have been a deliberate tactic from the Bulgarian's team to unsettle the often volatile Aussie.

"I feel Dani may have been asking though if Nick got a code violation for coaching that something like that might set Nick off," Hewitt said.

Kyrgios wasn't warned over the incident but coincidentally he was broken in the next service game, before going down in another tie-breaker as Dimitrov jumped to a commanding lead.