The shape of the day was already clear by lunch, when the visitors were 112-1 with McKinney unbeaten on 64.
Alex Lees was caught behind off Tom Bailey for three in the third over of the morning but McKinney and Gay had put on an unbroken 102 by the first interval, hitting 17 boundary fours on a pitch that justified Lees’ decision to bat first.
The afternoon began badly for Durham when McKinney, who had given two tough chances before he reached 50, played a horrendous flat-footed drive to a ball from Bailey and was caught behind by Matty Hurst for 71.
That wicket fell in the fourth over of the session and ended a 114-run stand for the second wicket but, as was the case in the morning’s play, an early wicket was a prelude to Durham’s domination.
Gay was joined by India’s Agarwal, who announced himself by pulling Mitch Stanley for a four and a six off successive balls. Gay reached his century off 156 balls when he stroked through midwicket for his 14th boundary four.
Agarwal brought up his fifty off 101 balls just before tea by which time Durham were 247-2 and the third-wicket pair had nearly doubled the score and put on 123.
The batters continued to bat serenely in the evening session and it was a surprise when Gay guided Walkden straight to Harris. But that wicket began a fine spell for Lancashire, whose left-arm spinner, Noman Ali, took the next two wickets.
Umpire Hassan Adnan judged that Colin Ackermann had edged a catch to Hurst on six but there was no doubt about the one to Josh Bohannon at cover that meant the departure of Agarwal for 66.
Those wickets left Durham on 306-5 but Ollie Robinson and Kasey Aldridge had steered their side to a third bonus point at the close. Noman finished the day with figures of 2-110.
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