Sri Lanka finished Day 1 on 88 for four, with the all-rounder on 27, after bowling out the hosts for just 178 in the first innings at the Hagley Oval.
"That first hour (on Day 2) is crucial," Southee said at the post match press conference. "(Mathews is) a class player. He's played a lot of test cricket and he's been out to New Zealand a number of times and is reasonably familiar with these conditions.
"He had a great start in Wellington, so he's flying high on confidence. He's a big wicket. I don't think we can put all our energy on him, there's still some quality guys to come as well."
After being sent to bat on a green wicket, the visitors looked like they would go on to dismiss the opposition for just under 100 at one stage. But Southee’s rearguard innings, supported with BJ Watling, helped the home side get past 150, with the duo stitching together 108 runs for the seventh wicket.
The key perpetrator on the day was Suranga Lakmal as the pacer went on to take a career-best 5 for 54 in an innings. However, Southee reckoned that the game is still in the balance.
"I think the way Lakmal bowled, he bowled exceptionally well and asked some tough questions.
"We've had other teams come to this part of the world and we've lost the toss and still been able to put a reasonable score on the board, so I think a lot of credit has to go to the way Lakmal bowled early on."
First Published: December 26, 2018, 1:59 PM IST