Pakistan 268 and 73 for 0 (Imam 42*, Shafique 27*) need 278 more runs to beat Australia 391 and 227 for 3 dec (Khawaja 104*, Warner 51)

Openers Imam-ul-Haq and Abdullah Shafique made a confident start in Pakistan's daunting chase of 351 to leave Australia anxious and the series deciding third Test tantalisingly poised ahead of the final day.

The historic three-Test series is headed for a gripping finish after Pakistan reached stumps on day four at 73 for 0 with Imam 42 not out and Shafique unbeaten on 27. They survived 27 overs as Pakistan requires another 278 runs for victory with a minimum of 121 overs to be bowled in the innings.

Shafique had a major scare on the second last day when he edged legspinner Marnus Labuschagne only for a wrong footed Steve Smith at first slip to desperately snatch his left hand out in vain. It continued a torrid time for Smith at slip and heightened Australia's nerves in the series finale after draws in Rawalpindi and Karachi.

Captain Pat Cummins had ended Australia's second innings at 227 for 3 shortly after tea in a bid to ensure plenty of time for his bowlers on a pitch playing tricks but is not a minefield. The declaration dangled a carrot to Pakistan, who defied the odds during their remarkable chase of 506 in Karachi when they finished at 443 for 7 from 171.4 overs.

This looms as another formidable challenge on a slow Lahore surface marked by low bounce with reverse swing and occasional sharp turn evident. History is against Pakistan with 208 runs being the highest successful fourth innings chase in Lahore while no team has survived more than 110 overs.

But Pakistan made a strong start after surviving a couple of close calls. Nathan Lyon, targeting the rough patches, had a huge shout for lbw turned down against Imam in the eighth over and reviews confirmed there was an inside edge. The offspinner then had Shafique caught behind in the 16th over only for Pakistan to successfully overturn the decision with replays showing the opener had missed a delivery that skidded on.

Lyon, who has traditionally struggled bowling Australia to victory on the final day, looms as a key figure particularly with legspinner Mitchell Swepson, in his second Test, looking ineffective so far this match.

Australia, however, should remain confident with the knowledge that batting has been harder in this match against the old ball, which Cummins and Mitchell Starc memorably reverse swung in Pakistan's first innings.

Up until Pakistan's response, Australia had dominated day four after taking a first innings lead of 123.

Usman Khawaja capped a series for the ages in his country of birth with an unbeaten 104 to notch his 12th Test century and second in the series. The remade opener has now scored fourth tons in nine innings since being recalled in January and has been the dominant batter in this series with 496 runs at 165.33. He was the only Australia batter to score a century in this series, the first between the teams in Pakistan since 1998.

Just before tea, in more celebrations for Australia, Smith smoked a boundary to become the quickest to 8000 Test runs in his 151th innings - one faster than Sri Lanka great Kumar Sangakkara.

Khawaja was earlier well supported by an aggressive David Warner, as the openers batted almost through the first session albeit aided by a sloppy Pakistan who appeared to be going through the motions.

Pakistan finally received a spark just before lunch when Shaheen Shah Afridi unleashed a spectacular delivery to uproot Warner's off stump in an unplayable ball leaving the opener to shake the bowler's hand on his way off.

Leading by 220 runs at lunch with nine wickets in hand, there was an expectation Australia would put the foot down in a bid to force an early declaration. As has been the case throughout the series, runs were hard to muster against the older ball although Australia didn't particularly look in any great hurry.

With wickets hard to come by for Pakistan, dashing their hopes of a fightback, a stalemate ensued for much of the second session with attention turning to when Cummins would declare.

Labuschagne, who had made two ducks twice in his last three innings, avoided a pair and made 36 before holing out attempting to lift the rate. It finished a relatively lean series for the No.1 Test ranked batter Labuschagne, who averaged 34 and remained without a Test century away from Australia.

The acceleration was left to Khawaja who memorably reached his ton just before tea to trigger jubilant celebrations.

After a disastrous final hour on day three, where they collapsed to lose 7 for 20, Pakistan were relatively toothless with the ball and in the field but there might be one last twist left in this long-awaited series.

Aided by a sporting declaration, Imam and Shafique have made the first steps in Pakistan's bid to conjure their second heroic fourth innings performance in just over a week.