Pursuing Australia's formidable total of 8-348 in Thursday's second match of the series, Imam-ul-Haq cracked his second century in three days and Babar hammered a 73-ball ton to fashion Pakistan's highest-ever successful ODI run pursuit.
Their dazzling efforts in Pakistan's 4-352 levelled the series at 1-1 and put McDermott's classy knock into the shade after he scored 104 off 108 balls.
But Pakistan, for whom Imam carved out 106 off 97 balls and Babar hammered 114 off 83, still needed another hero at the death as Khushdil Shah (27no off 17) smashed lusty blows off Nathan Ellis and Sean Abbott that ensured Pakistan got home on the last ball of the penultimate over.
The win topped Pakistan's previous best run chase - 7-327 against Bangladesh in Mirpur eight years ago - but left only a "bittersweet" feeling for 27-year-old McDermott.
For his century at Gaddafi Stadium had come in a losing cause, 32 years after his dad Craig McDermott snared 5-44 at the same ground to inspire Australia to an 18-run victory over Pakistan.
"Very bittersweet. I thought our total was enough but not to be," said McDermott.
"Really pleased with the way we batted, but we'll come again in two days time," he added, referring to Saturday's decider.
"It would have been really nice to finish off with a win tonight but, obviously, it's great to get a hundred - one of those milestones my father didn't pass."
Earlier, McDermott and Travis Head had tormented Pakistan for the second straight match.
McDermott had scored 55 in game one while Head, Tuesday's centurion matchwinner, fell just short of posting consecutive centuries when he was dismissed for 89 off 70 balls.
Marnus Labuschagne (59 off 49 balls) and Marcus Stoinis (49 off 33 balls) also joined in on the fun to leave Australia feeling they were in the box seat, especially after the innings had started with skipper Aaron Finch missing a full toss first ball and getting trapped lbw by Shaheen Afridi (4-63).
McDermott, who got into a heated verbal exchange with the fired-up Afridi, took 12 balls to get off the mark, but unleashed after that to finish with 10 fours and four sixes, while Head cracked six fours and five sixes.
Their departures didn't noticeably slow the run rate, with Labuschagne and Stoinis keeping the runs flowing.
But the Pakistan chase, McDermott conceded, was just much better paced than their slow-starting effort on Tuesday with Imam, who scored a ton in the first match, and Fakhar Zaman putting on 118 for the first wicket before the Babar show.
"We put up a good score, but Babar and Imam just batted beautifully tonight, you've just got to give credit where it's due," he shrugged.
None of the Australian bowlers really got to grips with the pair's mastery, with even Adam Zampa being hammered for 71 while taking the crucial wickets of Imam and Mohammad Rizwan.
McDermott, Head and Labuschagne were considered fringe ODI players before the current series, but their form will help boost their chances of becoming regulars leading into the 2023 50-over World Cup.
Their performances further showcased Australia's depth on a white-ball tour in which eight of their biggest players were absent.
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