Australian batter Steve Smith is "100 per cent" confident that his hand was under the ball when he attempted to catch India's Virat Kohli at second slip on the opening day of the fifth Test here on Friday.

However, the decision was referred to the TV umpire, who ultimately ruled Kohli not out.

"100 per cent; no denying it whatsoever, 100 per cent," Smith told 'Fox Sports' during the lunch break when asked if he had his hand under the ball.

"But the umpire’s made the decision and we’ll move on," he added.

The incident took place in the eighth over, off the first ball Kohli faced.

Kohli edged a length delivery from Scott Boland to second slip, where Steve Smith was positioned. Smith dived low to his right, seemingly catching the ball near the ground before flicking it upward toward gully, where Marnus Labuschagne completed the catch.

The on-field umpires referred the decision to TV umpire Joel Wilson, who, after reviewing replays showing the ball touching the ground before Smith scooped it, ruled Kohli not out.

Former ICC Elite Panel umpire Simon Taufel also weighed in on the incident, saying he understood Wilson's decision.

"I think you described it very well when you said that depending upon which side of the fence you sit on you could probably build a case for either decision to be given," Taufel told 'Channel 7'.

"Listening to Joel Wilson's language there, where he said the fingers were underneath the ball and then he's seen it roll on to the ground, by his own language he is telling us that he believes he's seeing that ball on the ground." He explained the situation, noting that according to ICC protocol on fair catches, if the fingers are seen beneath the ball, it is typically considered a fair catch.

However, he emphasised that there are no longer soft signals, and the TV umpire has the full authority to make the final call.

"So, there are two things that the TV umpire here is looking for. One is fingers underneath the ball. He was satisfied there. But then he believes through those pictures that he's clearly seen the ball on the ground. "And here's the challenge, slowing it right down with slow-mo. Play it at real speed and it looks pretty good. I can certainly understand what the third umpire's done there. He believes he's seen the ball on the ground and called it way he's seen it.

"Normally the ICC protocol on fair catches is if you see the fingers underneath the ball, that's good to maintain a fair catch. But here's the problem: the on-field umpire's no longer have the soft signal and make the decision, it's purely in the hands of the television umpire now," he added.

Kohli went on to make 17 before he was undone by an outside the off-stump delivery from Boland in the 32nd over.

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