"It's all about pressure," he noted after Pakistan crumbled from 71-2 to 117 all out in just 44.3 overs.
"Before this series I was saying that both teams had youngsters and the team that takes pressure well will win the game," Younis added.
"(Kumar) Sangakkara's captaincy (of Sri Lanka) was fantastic this morning -- if somebody else had captained they'd have come straight with a fast bowler and I was surprised when he opened with (Rangana) Herath."
"Our batsmen tried to play across the line and that is why they got into trouble," said Younis.
He was also unhappy that Pakistan had only secured a 50-run first innings lead despite at one stage being 294-5 in reply to Sri Lanka's 292.
NOT SUFFICIENT
"Our lead of 50 was not sufficient. We had (Mohammad) Yousuf and (Kamran) Akmal batting and we should have got a lead of 100 to 150," said Younis.
"It was the turning point that let them back into the game and gave Sri Lanka a chance."
However, despite his obvious disappointment, Khan backed his fledgling team to learn from the experience.
"The main thing is that we have a young team and it is not right to give them stick right away," he said.
"Because of the inexperience our team has not handled the pressure well, but we will pick up in the next two games."
He urged people not to burden exciting prospect Mohammad Aamer with high expectations after the 17-year-old's impressive debut with the ball. He took six for 112 in the match.
"Aamer is a young guy, but please don't compare him to Wasim Akram," Younis said.
"This is the problem in our country where whenever someone bowls well he is compared to Akram and then it becomes hard for me and for the player.
"Give him two to three years and after that we will talk about him," he added.
