Ireland, who qualified for the World Cup by finishing runners-up in the ICC Trophy in 2005, were regarded as minnows whose presence here among the top nations was scoffed at in some quarters.
However, they silenced the critics by dumping Pakistan out in the first round with a shock three-wicket win before playing a tied game against Zimbabwe to unexpectedly qualify for the second round Super Eights.
"People are entitled to their opinions but that sort of thing plays a large part in giving us motivation to do something special which we did," said Johnston after his team's 74-run win over Bangladesh here on Sunday.
Bangladesh themselves forced their detractors to eat their words by upstaging India in the first round and then inflicting a humiliating 67-run defeat on South Africa in the Super Eights.
"People said we shouldn't be in the Super Eights but again it gave us more motivation. We took those comments on board and it was like a mini World Cup for us against Bangladesh," said the Australian-born Johnston.
With Sunday's win Ireland have also notched a place in the ICC one-day rankings. They moved into 12th place after meeting the condition of beating two Test sides.
After the Super Eights have finished they will enter the rankings which are topped by world champions Australia and which feature Kenya, who were knocked out in the first round in the World Cup, in 11th spot.
"It's a great achievement. If you look through the history books then you will see Sri Lanka were introduced to one-day cricket in the early 1980s and they won the World Cup 10-15 years later. They turned one-day cricket on its head," said Johnston.
"Bangladesh beat Australia in 2005 and have beaten South Africa here. Kenya made it to the semis in the last World Cup, so we had to prove a point and turn around Friday's disappointment," added Johnston of a nine-wicket mauling from Australia.
"We set ourselves some serious goals against Bangladesh and the first was to win the toss which I did, and then see off the new ball," said Johnston whose openers laid the foundation of their 243-7 total with a stand of 92.
The good work of William Porterfield (85) and Jeremy Bray (31) was further boosted by Kevin O'Brien (48) and Johnston (30).
They then bowled Bangladesh out for 169 in the 42nd over.
"We have a pretty big game against Sri Lanka on Wednesday. That will be the last game for (coach) Adrian Birrell, and it would be fitting way for us to send him off by putting on another display like this."
Birrell, who leaves the job after the World Cup, said he was proud of his team.
"We have got a great squad of players and there is a wonderful team spirit," said South Africa-born Birrell.
"Five years ago we were ranked below Denmark and now we are ranked above all the Associates and that is very satisfying.
"I am very proud of the five years I have spent with Ireland and it has been a great experience. They made me feel as one of their own."
Once the World Cup is finished, Birrell will be succeeded by former West Indies Test player Phil Simmons