"If the batsmen get themselves in, as the ball gets older it's a lot easier to bat. Throughout the game when the Sri Lankans bowled there hasn't been a lot of reverse swing. It's a nice wicket to bat on.''
Southee said the Black Caps hadn't talked about a minimum total, rather it was a case of batting for time.
"If we can bat all day tomorrow it will go a long way in setting up a very good second innings score.''
As for his form with the ball, Southee would say only: "It's a learning curve. I've had some very poor tests in the last couple of years and was out of the test side at the start of the year so it's good to be back and taking wickets.''
Captain Ross Taylor had talked about the threat New Zealand's seamers could represent after England's recent success in Sri Lanka, but even he must have been surprised by the new ball deeds of Southee, Trent Boult and Co.
Southee's first wicket came on the fourth ball of the day, getting Tharanga Paranavitana to play on to reduce Sri Lanka to 9-2. With both openers gone for ducks the heat fell on the Sri Lankan middle order and, like their Kiwi counterparts, they failed to deal with the pressure.
Southee used his swing to terrorise Suraj Randiv, finding the outside edge on consecutive balls with identical out-swinging deliveries. The first edge flew straight to McCullum at third slip and, after he dropped a simple catch, Martin Guptill snagged the second much to McCullum's relief.
Boult then chimed in with the prized wicket of Kumar Sangakkara, claiming the veteran batsman for five to add to an impressive list of career scalps already boasting Chris Gayle, Jacques Kallis and Sachin Tendulkar.
Southee struck Thilan Samaraweera on the pad to complete a fine first hour and make bowling advisor Chaminda Vaas appear an inspired hire but, just when the Black Caps were threatening to skittle Sri Lanka, Mahela Jayawardene and Angelo Mathews came together.
James Franklin was the man who broke the 156-run partnership when dismissing Mathews for 79.
Patel struck a short time later to remove Prasanna Jayawardene for four before grabbing his second, getting Mahela Jayawardene for 91.
Once Patel took his third, the introduction of the new ball finished off the hosts' innings when Boult claimed his second scalp with just his second delivery.