Sri Lanka trounced top-ranked Pakistan 3-0 after a 13-run victory in the third and final Twenty20, in front of 27,000 fans at the Gaddafi Stadium, in Lahore, on Wednesday.
Needing 54 runs off the last five overs, with eight wickets in hand, Pakistan again stumbled in its run-chase for the third successive time in the series and were restricted to 134-6.
Sri Lanka won the first match by 64 runs and then beat Pakistan by 35.
Leg-spinner Wanindu Hasaranga claimed three wickets in two overs to finish with 3-21 and also grabbed a well-judged catch at long-on boundary to dismiss dangerman Imad Wasim as Pakistan batting crumbled in the last five overs.
Earlier, after winning the toss and electing to bat first, a second-string Sri Lanka scored 147-7 despite resting five players who had featured in the two earlier victories.
“Unity was the secret (of success)," Sri Lanka captain Dasun Shanaka said after leading his team on a victory lap around the stadium.
“We wanted to thank the people of Pakistan, they supported us, not just the Pakistan (team). All the players were bonded and that was the key to our success."
The series sweep by a young Sri Lanka team was made even more impressive by the fact that it toured Pakistan without several key players, who pulled out due to security concerns.
Debutant Oshanda Fernando, one of the five changes Sri Lanka made, held the innings together with a gritty unbeaten 78 off 48 balls as Mohammad Amir was the only bowler to show some resilience by claiming 3-27.
Fernando dominated a 76-run stand with Shanaka, whose contribution was only 12 but the partnership pulled Sri Lanka out of trouble from 4-58.
In the absence of rested frontline seamers Isuru Udana and Nuwan Pradeep, Sri Lanka seamers Kasun Rajitha (1-17) and Lahiru Kumara bowled with disciplined line and length and never allowed Pakistan batsmen to go for big hitting.
Haris Sohail, playing his first match of the series, made 52 off 50 balls and Babar Azam scored 27 before Hasaranga turned the tables in his team's favour by having Sohail stumped off the first ball in the 16th over.
"We were subdued, we didn't express ourselves throughout this series," conceded Pakistan captain Sarfaraz Ahmed, who was yet again clean bowled by Hasaranga.
"We need to work a lot in all three fronts, especially fielding. We can't beat any team if we drop catches like that in the middle overs."
Sarfaraz himself dropped a simple catch off Sadeera Samarawickrama and also missed down the leg side stumping of Shanaka when the Sri Lanka captain had scored just 1.
Shadab Khan missed a skier which could have ended Bhanuka Rajapaksa on 1 in Amir's second over, while the Pakistan fielders also missed out several run-out chances.
But Fernando, who hit eight fours and three sixes, gave Sri Lanka enough runs to defend as he kept putting Pakistan bowlers under pressure. The left-hander was especially ruthless against left-arm seamer Usman Shinwari, who gave away 43 runs off his four overs without a wicket while leg-spinner Shadab also leaked 32 runs off his four wicketless overs.
Sri Lanka lost the preceding one-day series 2-0 but completed an upset in the Twenty20s by clean sweeping a three-match series for the first time.
It is the first time since Sri Lanka's team bus was attacked in Lahore in 2009 that a foreign team conducted a two-week tour of Pakistan.
Major teams have avoided the country since the ambush that killed eight people and injured several players.