Ton-up McDermott propels Australia to 348-8 in second ODI
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All-rounder Marcus Stoinis added the finishing touch with a quickfire 49, with five boundaries and a six.
Pace spearhead Shaheen Shah Afridi -- who missed Pakistan's 88-run defeat in the first ODI with a knee injury -- gave the home side a breakthrough off the third ball of the innings when he trapped Aaron Finch leg-before without scoring.
But Australia scored at will after that with McDermott and Head adding 162 off 144 balls for the second wicket, hitting boundaries with ease.
Head, who scored 101 on Tuesday, smashed five sixes and six fours before miscuing a sweep off leg-spinner Zahid Mahmood, being caught by Shaheen at short fine-leg.
McDermott added another 74 with Labuschagne, and during that stand hit spinner Khushdil Shah over long-off boundary for six to complete a century off 102 balls.
He was finally caught off pacer Mohammad Wasim.
Despite Alex Carey and Cameron Green falling for five each, Sean Abbott chipped in with a 16-ball 28 to boost the total.
Shaheen finished with 4-63 and Wasim took 2-56, but Pakistan's Iftikhar Ahmed and Khushdil Shah conceded 95 runs in ten overs between them.
The third and final match is on Saturday, also in Lahore.