Sri Lanka face New Zealand again after losing the ICC World Cup. We certainly expect an interesting match between the two teams in this Test match, moreover Sri Lanka team's current performance is very good, in which case they will definitely play well against New Zealand. Moreover, Sri Lanka team achieved a great win against England in the last match, so there is definitely hope for a win against New Zealand. However, although New Zealand are favorites to win the series, it will be difficult for New Zealand to win the match against Sri Lanka.
But the difference I see between these two teams is that Sri Lanka's win is pretty much assured as they are playing at home.

Sri Lanka team won the toss and decided to bat which is a good decision for Sri Lankan team, Test match is usually a long game where strategy should be used. And Pathum Nishanka, Dimuth Karunaratne entered the field as the opening batsmen of the Sri Lankan team but could not build their batting partnership. As the opening two batsmen got out after collecting only a few, the Sri Lankan players did not perform well on their own ground.
Thus, if the Test match continues to lose wickets, then there is a possibility of an all-out in the first innings, as the two experienced batsmen of the Sri Lankan team were dismissed early on, leaving the team under a lot of pressure. If they can't perform well at their home ground then they won't be able to win the first and first match. If the Sri Lankan team players are weak in terms of batting from the beginning then the chances of performing well later on will be very low.