The pace duo never allowed Pakistan, who won the toss and batted, to play freely on a Dubai stadium pitch which had good carry and bounce, with only opener Ahmed Shehzad (58) batting with any authority.
Mohammad Hafeez (26), Shahid Afridi (26) and skipper Misbah-ul Haq (25) also got starts but did not capitalise for Pakistan to put together a challenging total.
Just like the first match, which South Africa won by one run, Pakistan lost opener Nasir Jamshed in the third over of the innings when the left-hander failed to keep a pull shot down and was smartly caught at fine-leg by Lonwabo Tsotsobe.
Shehzad then steadied the innings during a 48-run second wicket partnership with Hafeez and another 60 for the third wicket with Misbah before McLaren derailed the innings with a double strike.
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Hafeez played on and was bowled in McLaren's first over.
Misbah, when on eight, completed 1,000 one-day runs in 2013, becoming the third batsman to achieve the milestone after Australia's George Bailey and India's Virat Kohli.
But Misbah too perished in rather soft fashion, flicking McLaren straight into the hands of mid-wicket. He hit a boundary and a six off 44 balls.
Shehzad hit four boundaries off 85 balls.
Umar Amin (14) and Umar Akmal (18) took Pakistan to 148 and into the power-play but both fell at the same score, Umar hitting Morkel straight into the hands of point while Amin edged McLaren's slow delivery to wicket-keeper AB de Villiers.
Afridi hit four boundaries off 20 balls while Wahab Riaz hit two sixes in his 18.