An expectant crowd has cheered like Steve Smith scored a century after the Australian batsman took 45 minutes to score his first run at the SCG.

In an extraordinary display of patience against New Zealand, Smith batted away or left 38 balls before he decided to go for a single on his 39th.

It was a record wait to score for Smith in a Test innings and, after much anticipation, the crowd stood to applaud.

The sequence of events reminded former Australian No.11 batsman Glenn McGrath of Indian bowler Ajit Agarkar's time in Australia.

"I was trying to think when there was last a cheer for one run, and it was Ajit Agarkar here in 1999-2000," McGrath said on Channel 7.

"He scored a run, but that was after five zeros in a row - so a little bit different!"

Smith, who was already on his fourth pair of gloves in the innings, quickly added more runs to his tally and hit his first boundary in the following over.

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His go-slow came in response to being dismissed by New Zealand bowler Neil Wagner twice in Melbourne.

Smith has had a largely torrid time against Wagner, with short balls proving problematic for the world's No.1 batsman.

"We are seeing something rather extraordinary unfold at the SCG," Channel 7 commentator Alison Mitchell said while Smith was still on naught.

"Smith has never looked less like he is in a bubble. Everything has been distracting him, he has been noticing everything."

He arrived at the crease after David Warner (45) was caught on the leg side off the bowling of Wagner.

While Smith held back, Marnus Labuschagne continued to push on and later reached another half-century in his golden summer.