Tournament hosts and favourites England were beaten by 14 runs at Trent Bridge on Monday as Pakistan ended a run of 11 straight losses in completed ODIs – a sequence that included a 4-0 series thrashing at the hands of Eoin Morgan's men and a 5-0 whitewash in the United Arab Emirates against Australia.
Having been rolled out for just 105 in their opening World Cup game against West Indies, Pakistan's subsequent victory against England was all the more impressive and Flower believes they have shifted a significant psychological burden ahead of facing Sri Lanka at Bristol County Ground on Friday.
"Yeah, I definitely do sense quite a bit of confidence, especially in the meeting we had this morning," Flower told a news conference.
"Since we have won, it took off a lot of the pressure, definitely, having gone through those string of defeats.
"Psychologically, that lifts a huge weight from their shoulders. And to score 350 against a very good England attack, the guys are relieved."
— Pakistan Cricket (@TheRealPCB) June 6, 2019
Sri Lanka, meanwhile, come into the meeting on the back of a 34-run DLS win over Afghanistan, having been thrashed by 10 wickets at the hands of New Zealand in their opener.
"Pakistan is an unpredictable team, but we also have a bit of confidence so we will be trying to give it our best shot," said captain Dimuth Karunaratne.
"We are not over-confident but we are trying to do our best. We will see tomorrow."