In their partial defence, at 40 for three, it was necessary to knuckle down and try to put some pegs in the ground. Left-arm spinner Rangana Herath was impressive. He was on in the 18th over and bowled just about unchanged from then on, his five for 65 off 30 overs a good reward for thoughtful bowling.
McCullum praised the 34-year-old, who took his 11th five-wicket bag in his 41st test, and saluted Sri Lanka's nous when they put the squeeze on New Zealand's batsmen. Even so ...
"When the game is delicately poised we need to be slightly more positive and try and grab the situation, rather than let the opposition dictate terms," McCullum said.
He ruled out the notion that players find it hard to switch between the three forms of the game. He pointed out that several of the New Zealand squad had been playing four-day cricket before arriving for the tests, "so they're very well prepared and the rest of us are pretty adaptable in terms of being able to change formats".
Yes, the pitch had taken turn, but it was slow, and didn't really bite, and in any case "that's what you expect when you come to the sub-continent".
McCullum was able to display his more measured side, as distinct from the T20 flier, taking 125 balls over his 68. Flynn took 152 for his 53 before trying to cut a wide ball just before tea, which was a significant loss.
New Zealand will bat again in this test, weather permitting. They'll need to be far surer of themselves, and trust their ability.