Pakistan's decision to bat first despite the McLean Park pitch appearing to favour the seam bowlers for the first time in recent history looms as a massive misjudgment as a retirement-bound O'Brien cut a swathe through the tourist's top order.
At one stage O'Brien had figures of four for three from five overs before Pakistan went to lunch on 83 for five, with opener Imran Farhat on 47 and vice-captain Kamran Akmal unbeaten on 18.
O'Brien, who ends a 22-test career here before moving to England, started his rout with his fifth ball when Faisal Iqbal's recall at the expense of Shoaib Malik lasted all of six runs before a lifting delivery caught the splice and ballooned to Martin Guptill in the gully.
The 33-year-old then removed Pakistan's batting dangermen -- captain Mohammad Yousuf and Umar Akmal -- without scoring before Misbah-ul-Haq added a third duck to a sorry scorecard.
Yousuf, never at ease during his 13-ball stay, was guilty of playing away from his body to give Tim McIntosh a sharp catch at second slip.
Umar, a centurion on debut in the first test in Dunedin, recorded the first duck of his fledgling career when his loose shot sparred to Guptill, again in the gully. Four balls later Misbah joined the procession when wicketkeeper Brendon McCullum gloved a straight forward edge as Pakistan plummeted to 51 for five in 19 overs.
O'Brien did not concede a run until his fifth over and ended the session with the analysis of four for 15 from eight overs.
Southee, who turned 21 today, justified his inclusion as the fourth seamer with his 10th delivery when opener Salman Butt, on nine, had his middle stump uprooted after trying an ambitious stroke through mid wicket.
Farhat took a nasty blow on the upper arm from Daryl Tuffey and was also rapped on the glove by O'Brien but at least the left-hander got to lunch, his 70-ball innings so far containing eight boundaries.
