Thisara important to team balance - Mahela
Sri Lanka have struggled to penetrate with the ball on New Zealand's truer, bouncier surfaces, and have also been light on batting power at the death. Thisara is capable of alleviating those concerns, but has recently been underwhelming in both major disciplines. He played all seven bilateral matches against New Zealand, and collected four wickets and had a high-score of 20.
Thisara's form has subsided since his outings against Pakistan in August, when he was the player of the three-match ODI series. He had also been destructive with ball and bat in Australia, on past tours.
"Thisara is a vital part of our team, and he still hasn't come right in New Zealand," Jayawardene told ESPNCricinfo. "If we can have Thisara batting well and bowling well, he's a match-winner. He has proven that with the amount of man-of-the-match awards he's won. Right now he's trying to find that form."
Thisara was not picked to play in Sri Lanka's tournament opener against New Zealand, and Sri Lanka have sought to bolster the middle order by batting Dimuth Karunaratne at no. 5. That position would seem a poor fit for Karunaratne, who is a Test opener by trade, but Jayawardene was wary of displacing men from the experienced top order for the purpose of batting Karunaratne at a more familiar position.
"I don't know if changing the line up is the solution," Jayawardene said. "Dimuth has been given a role to play and he should have the confidence to do that. Lahiru Thirimanne going up the order did require a change, but if we try to patch that by moving batsmen around, we might have problems in a different area. The top four or five guys are batting really well, so we've been getting good starts, which are important. In the middle order, I thought Jeevan Mendis was batting well in the lead-up games, and he's given us a little bit of balance."
Sri Lanka lost both warm-up encounters, including the game against Zimbabwe, before losing the tournament opener to New Zealand by 98 runs. Jayawardene conceded it had been a slow start to the campaign, but said Sri Lanka had the quality and the know-how to win the tournament, so long as they played well.
"No one gives us any chance in any tournament," he said. "Even back home, people don't really rate us that high. We've come across that often, we've fought hard, and we've proven a lot of people wrong. We knew that playing these teams in these conditions was going to be tough. We will have our fair share of defeats - that's a given. It's not a tournament that you can completely dominate. But the idea is to win those crucial moments and crucial games and get to a position where we can strike.
"We know handling big tournaments is about not panicking. It's nothing crazy. It's about building on the things we've been doing for years. In the crunch games, you just have to hold everything together. You shouldn't put added pressure on yourself, because that restricts the way you play. We know we have handled tough situations in big finals, so that belief is there."
Andrew Fidel Fernando is ESPNcricinfo's Sri Lanka correspondent. @andrewffernando