While Sri Lanka were bowled out for mere 136-runs against the New Zealand, they crumbled from 144/1 to 201 all out against Afghanistan on the same pitch. Sri Lankan middle-order failed to fire in both the games.
"If we make a good start to the innings then we can keep that momentum going. If you take the last couple of games, we couldn't capitalise on the starts we made.
"We need those middle order contributions and I think that's the key for us as a batting line-up. Other than that, I think as a group we're doing really good," Karunaratne was quoted as saying by ICC media.
The match between Sri Lanka and Pakistan was called off without a ball being bowled because of persistent rain at the Bristol County Ground on Friday.
The no-result meant the points were shared between the teams, pushing Sri Lanka and Pakistan into third and fourth place, respectively, in the table.
"We all came here to play cricket so it's not good that we didn't get to play. We're really disappointed as a team but we'll look ahead to the next game.
"We won our last game against Afghanistan and while we may lose some matches along the way during the World Cup, we always give a lot of fight and that's all we want," said the skipper.
Sri Lanka, the 1996 champions, are now looking ahead to their clash against Bangladesh here on June 11.
"We want to compete with the other teams. We did really well against Afghanistan to get the win and I want us to take that confidence into the rest of the matches, starting with Bangladesh," said Karunaratne.