Darkening skies saw the ECB/MCC power bill take another hit with the lights coming on. The players eventually came off early due to rain.
England showed resilience despite McCullum trying myriad fielding options including a mini-ring around Root from Trent Boult. Spinner Mark Craig struggled to put pressure on due to some erratic lengths. An lbw review against Cook on 102 failed to elicit a wicket. Tim Southee was the best of the New Zealand bowlers, taking two for 61 from 18 overs.
England dominated the opening session, courtesy of Cook and Root. Both cocooned themselves in concentration. England's pluck should guarantee an absorbing denouement tomorrow.
Southee had Ian Bell caught by stand-in wicketkeeper Tom Latham with the day's third ball. It angled away in perfect symmetry as Bell's bat committed. England were 74 for three and New Zealand's advantage grew.
Root, on seven, clipped a Boult delivery to Corey Anderson at square leg in the 32nd over. Despite Anderson's gallant effort, doubt remained after replays. Root, a player averaging 94.84 from his 17 previous innings in the last 12 months, survived. It was a fair call too, considering Root was denied a catch in similar circumstances at gully on Saturday. The doubt went in favour of the batsman.
Cook cutting Craig's third ball of the morning past backward point for four was also significant. It took England to 135 for three and, importantly, into credit.
Once a team's in credit in the third innings, Lord's can make the experience dicey for their opponents.
New Zealand fans must steel themselves. In 130 tests across 131 years at the ground there have been 35 successful fourth innings chases, including New Zealand's 58 in 1999 to secure their solitary win in 16 attempts. However, only three successful chases have been in excess of 200 and six have been better than 150.
Compounding this is New Zealand's failure in their last attempt chasing 239 in 2013. Stuart Broad took seven for 44 and they were dismissed for 68, their third worst total at the ground.