Pakistan edged out Sri Lanka by three wickets in a thrilling last-over finish in the first match on Wednesday.
If Pakistan, currently fourth, win on Friday they will displace Sri Lanka as number one team in the Twenty20 rankings.
But Chandimal said his team was working hard to bounce back.
"Pakistan have played some good cricket in South Africa recently and we never underestimated them, especially in limited over cricket, so we will put our heart and soul and come back strongly," he said.
Sent into bat, Sri Lanka rode on a brilliant 34-ball 50 by Angelo Mathews.
Pakistan chased down the target off the first ball of the 20th over with Shahid Afridi hitting paceman Nuwan Kulasekara out of the ground, scoring a fiery 20-ball 39 not out.
Chandimal, who made 22 but wasted a good start, admitted his team were short of an ideal total.
"I think we were 10-15 runs short. The ball was coming nicely to the bat. After that, bowlers did not bowl in right areas.
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