Younis Khan claimed his 34th Test century and first in Australia to keep Pakistan's first innings barely alive in the final Test in Sydney on Thursday.

The 39-year-old Pakistan great became the first batsman to score Test hundreds in 11 countries as he turned around an indifferent series with his first century since October.

He fought back from a dreadful mix-up which led to the run-out of the team's leading scorer of the series, Azhar Ali, to spearhead the Pakistan fightback on a rain-affected day three.

Younis went to stumps on 136 off 279 balls with the tourists still trailing Australia by 267 runs and 68 from avoiding the follow-on. Pakistan were 271 for eight with Yasir Shah five not out.

Younis showed Australia his undoubted quality with 15 fours and a six off Nathan Lyon, with his century coming off 208 balls.

In 206 Test innings, Younis has only been dismissed once in the 90s with 91 against New Zealand in Auckland in 2001.

While Younis held court, skipper Misbah-ul-Haq continued his hapless series when he holed out to deep mid-wicket off Lyon.

Tellingly, his 18 was his highest score of a series in which he has totalled just 38 runs at a paltry average of 7.60.

Azhar was run out for 71 in a poor piece of running with Younis, when he could not beat home Mitchell Starc's throw from mid-on to the striker's end.

Younis drove Lyon to a diving fielder at short midwicket and hesitated, leading to some indecision with Azhar before Starc swooped in to throw back to the 'keeper.

In the process Azhar passed Mohsin Khan (390) as Pakistan's highest scorer in a series in Australia, but he achieved it in three Tests, compared to Mohsin's five Tests in 1983.

In five innings, Azhar has scored 395 runs in this series at 98.75.

Azhar and Younis put on 146 runs for the third wicket, restoring the Pakistan innings after they were six for two.

Asad Shafiq was out when Younis was on 99 after he played well forward to left-arm spinner Steve O'Keefe and got an inside edge for Steve Smith to take a fine outstretched right-hand catch for four.

It was Smith's eighth catch in what has been a brilliant fielding series for the Australia skipper.

Sarfraz Ahmed was caught in the gully off Starc for 18 late in the day and Mohammad Amir played a rash shot to be caught in the deep off Lyon for four.

Lyon grabbed a third wicket when he bowled Wahab Riaz for eight in the day's penultimate over.

Wicketkeeper Matthew Wade was forced to leave the field with a stomach illness shortly after play got underway in mid-afternoon following rain, with Peter Handscomb deputising for him as he sought treatment.

Cricket Australia said Wade was suffering from diarrhoea and nausea. He fell ill in the morning and returned to the team hotel to rest, but was expected to recover in time for Friday's play.

First-innings centurion Matt Renshaw left the field after being struck on the helmet at short leg and was assessed for concussion.

Australia have already won the series after victories in the Brisbane and Melbourne Tests, while Pakistan are battling to avoid their 12th straight Test defeat in Australia.