McCullum has his ninth test century, Watling his seventh test 50 and for the captain the job remains all in front of New Zealand.
"We have got a lot more ground to cover tomorrow," he said last night.
"We know we have so much more hard work to go.
"Being five down was key for us. If we had been six or seven down I think the test was over. It was a big couple of hours at the end of the day."
New Zealand have been setting the tone for most of the summer. This test has been different, which makes McCullum and Watling's performance all the more creditable.
McCullum is clearly battling physical fitness issues but dug deep and with Watling a faithful lieutenant they have, at the least, made India work for what would be a series-equalling victory today.
They'll need a pile more runs; batting conditions are good. Jimmy Neesham and Tim Southee will almost certainly be needed to make solid contributions.
If - and it's a big if even after yesterday afternoon's substantial achievement - New Zealand can build a lead of 200 they will at least have something to work with.
The first session was grim.
In Ross Taylor's absence, Kane Williamson needed a long innings. Instead he got a faint touch to the 10th ball of the day.
Hamish Rutherford and Tom Latham, after an encouraging 1h 51min in his second test innings, were gone before lunch, and Corey Anderson to a disappointingly soft shot shortly after.
McCullum, playing an uncharacteristic innings - he's grafted a tick under six hours for his 114 off 237 balls - and Watling, 4h 19min and 208 balls over his 52, have shown considerable backbone in difficult circumstances.
There were close shaves along the way. McCullum was dropped twice, and both were beaten outside off stump.
Zaheer Khan was the pick of India's bowlers, but fielding let the tourists down yesterday.
Baz's batting
*Brendon McCullum's century is his ninth in tests, second in consecutive tests and third of the home summer.
*McCullum's unbroken sixth wicket stand of 158 with BJ Watling broke the old mark against India, 137 by Craig McMillan and Chris Cairns, at Wellington in 1998-99.
*McCullum is the fourth New Zealander after Stephen Fleming, Martin Crowe and John Wright to pass 5000 test runs; Watling went past his 1000 yesterday.