Australian skipper Steve Smith has joined Don Bradman as one of four players to average more than 60 through 50 Tests.

On a record-breaking fourth day against Pakistan, Smith took a step towards batting immortality with another half-century in the second innings.

He was eventually brought undone by Yasir Shah after a 43-ball 59 that included eight boundaries and a six, leaving him with a series-high 441 runs.

But more significantly, his average remained above the 60-run mark at 60.15, emulating Bradman and England pair Herbert Sutcliffe and Jack Hobbs after 50 Tests.

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Smith's rapid-fire knock - in his 50th Test - on Friday means he also holds the highest mark of any batsman in Test history through a minimum 92 innings.

Just five players hold a higher overall average than the 27-year-old - including Don Bradman's famous 99.94 - but none played as many innings.

Bradman amassed 6996 runs from 80 innings.

The accomplishments mark another remarkable chapter in the 27-year-old's already great career that began when he debuted as a leg-spinning allrounder batting at No.8.

Now with 4752 runs from 92 innings, he is on track to become the third Australian behind Bradman and Matthew Hayden to register 5000 Test runs in less than 100 innings.

His deeds are more incredible given he didn't reach three figures until his 12th Test.

But with centuries against every Test nation he's played against - 17 in all - and an average of 76.03 since assuming the captaincy, Smith is carving out of the all-time great Test careers.

Smith hits rarified air in the same match Warner became only the fifth player in history to rack up a century before lunch on the opening day, and smacked the second fastest half-century.

- AAP