Jos Buttler???s 55 not out led England to a five-wicket victory but they still trail the hosts 2-1 in the seven-match series.
The victory was a welcome boost to the side, who have been under fire for their one-day performances this year ahead of the World Cup in Australia which starts in February.
Morgan insists the win has changed the mind-set of the players and expects more positive displays in the future.
???In a seven-match series you never look to far ahead but you can see the belief in the guys??? eyes that they gained a lot of confidence from the other night.???
Morgan will replace regular skipper Alastair Cook, who is serving a one-match ban for a slow over rate, despite his form also being a huge concern for the coaching staff.
Head coach Peter Moores hopes the added responsibitly will aid Morgan???s game but the player has his own theory to improve his scores.
???I think I need as much time out in the middle as possible,??? he said.
???If I chew up balls in the middle period then so be it but there has not been one particular way I???ve been getting out which creates a problem in that you can???t pinpoint what you???ve been doing wrong so more time at the crease will help improve my form.???
Morgan also has sympathy for Cook due to the poor weather conditions in Hambantota on Wednesday but admits the team must improve in getting through their overs as quickly as possible.
???We need to be quicker at bowling overs, it???s as simple as that,??? said the Middlesex batsman.
???The other night was a really difficult situation because everytime the ball got hit over the commercial boards the ball was soaking and we had to take time to dry it.
???I know a little bit of dispensation was given but for him (Cook) that was difficult. We have talked about it so hopefully we will get better at it.
???Steven Finn takes four and a half to five minutes to bowl an over when the average is usually under four and everything chips away at our time. Finny is aware of it and when the spinners are on we need to quicken up the pace.