"With the new ball, it's nice to bowl and we had it swinging so we were lucky to pick up a few wickets there.''
Southee, who picked up three of his own, is probably being modest when he mentions fortune playing a part. The opening spell of bowling by he and Trent Boult was as ferocious as new ball bowling comes, with both men causing India's top order continual problems.
Southee, recalled to the side in place of Chris Martin, said he enjoyed bowling in tandem with his Northern Districts teammate, something the pair should expect to do a lot more often.
"I've played a lot of cricket with Trent through age group and domestic. It's always good to have those guys that you've bowled a lot with in previous years.
"It was a good spell with the new ball from both of us.''
Once Southee dismissed Gautam Gambhir and Cheteshwar Pujara, and Doug Bracewell chimed in with the wickets of Virender Sehwag and Sachin Tendulkar, India began to fight back.
Filling spots five through seven in a stacked batting order, Suresh Raina, Virat Kohli and MS Dhoni showed the top order how it was done, though Southee thought that had more to do with conditions than anything.
"The wicket's a pretty good wicket and India came back well after lunch as the ball got a bit older,'' he said. "As the ball gets older it gets a bit softer and loses its bounce, it is a bit easier to bat.
"We were still creating chances, we were still getting edges. We just didn't build up enough pressure through dots and the edges, with the ball a bit softer, weren't quite carrying.''
Southee said, with the wicket at M Chinnaswamy Stadium remaining in good condition, the match was evenly poised.
"If we can pick up the wickets tomorrow without too much damage and if we can put some runs on the board, then we're right in it.''
Though, he did sound a word of warning for a batting unit that has found India's spinners unplayable at times. Ravi Ashwin took 12 wickets in the first test in Hyderabad and Pragyan Ojha already has five scalps to his name in this match - a trend Southee expected to continue.
"It's turned the whole way through and I guess that will be a massive part in how well we bat in our second innings. "