Pakistan piled up 175-5 after electing to bat and then restricted the reigning World Twenty20 champions to 146-7 in the day-night match at the Premadasa stadium.
Akmal hit three boundaries and as many sixes during an entertaining fourth wicket stand of 81 from just 45 deliveries with Shoaib Malik, who remained unbeaten on a 31-ball 46.
Ahmed Shehzad was the other notable contributor with 46 off 38 balls, but Sri Lanka lost the way when Pakistan plundered 70 runs in the final six overs to set up the challenging target.
Pakistan lost opener Mukhtar Ahmed in the second over, but Shehzad and Mohammad Hafeez revived the innings with a 42-run partnership for the second wicket.
Debutant left-arm seamer Binura Fernando conceded 17 runs in the 16th over which included two consecutive sixes by Akmal.
Sri Lanka’s captain Lasith Malinga was the most expensive bowler, giving away 46 runs in his four overs.
The hosts were dealt early blows as Kusal Perera fell off the third ball of the innings and Tillakaratne Dilshan was dismissed in the next over to make it 13-2.
Debutant Dhananjaya de Silva looked promising during his knock of 31 and another youngster Milinda Siriwardana made 35, before Chamara Kapugedera justified his recall with three sixes in his unbeaten 31 off 16 balls.
Tanvir, the left-arm seamer, finished with three for 29 and Anwar Ali took two for 27 to tie down the Sri Lankan batsmen.
The second match will be played at the same venue on Saturday with Pakistan looking to complete a triple on the current tour, having earlier clinched the Tests 2-1 and the one-dayers 3-2.
The tourists, who piled up 175-5 after electing to bat, restricted Sri Lanka to 146-7 in the day-night match at the Premadasa stadium.
Full scoreboard of the first Twenty20 international between Pakistan and Sri Lanka at the Premadasa stadium in Colombo on Thursday,
K. Perera c Afridi b Anwar 4
T. Dilshan c Rizwan b Tanvir 6
D. de Silva c Shehzad b Malik 31
K. Vithanage b Tanvir 1
A. Mathews b Imad 23
M. Siriwardana c Anwar b Tanvir 35
C. Kapugedera not out 31
T. Perera c Rizwan b Anwar 2
B. Fernando not out 8
Extras: (b1, lb3, w1) 5
Total (for seven wickets, 20 overs) 146
Fall of wickets: 1-4 (K. Perera), 2-13 (Dilshan), 3-19 (Vithanage), 4-55 (Mathews), 5-92 (de Silva), 6-116 (Siriwardana), 7-121 (T. Perera).
Bowling: Anwar 4-0-27-2 (w1), Tanvir 4-0-29-3, Irfan 4-0-25-0, Afridi 4-0-31-0, Imad 3-0-21-1, Malik 1-0-9-1.
Mukhtar Ahmed c Vandersay b Mathews 2
Ahmed Shehzad c Malinga b T. Perera 46
Mohammad Hafeez c Vithanage b T. Perera 17
Shoaib Malik not out 46
Umar Akmal lbw b Malinga 46
Shahid Afridi b Fernando 8
Anwar Ali not out 0
Extras: (lb3, w7) 10
Total (for five wickets, 20 overs) 175
Fall of wickets: 1-10 (Mukhtar), 2-52 (Hafeez), 3-83 (Shehzad), 4-164 (Akmal), 5-175 (Afridi).
Bowling: Fernando 4-0-38-1 (w3), Mathews 4-0-33-1 (w2), Malinga 4-0-46-1 (w2), Vandersay 4-0-25-0, T. Perara 4-0-30-2.
After 20 Over
After 19 Over
Pakistan 164/4 (RR: 8.63)
After 15 Over
Pakistan 116/3 (RR: 7.73)
Shoaib Malik 28 (19b 3×4 0x6)
Umar Akmal 14 (11b 1×4 0x6)
After 13 Over
Pakistan 90/3 (RR: 6.92)
Ball-by-Ball: 1 • 1 1 1 1
After 12 Over
Pakistan 85/3 (RR: 7.08)
Ahmed Shehzad c Malinga b NLTC Perera 46
Ball-by-Ball: 4 W • 1 1
After 11 Over
Pakistan 79/2 (RR: 7.18)
Ball-by-Ball: 1lb 1 1 2 2 1
After 10 Over
Pakistan 71/2 (RR: 7.10)
Ball-by-Ball: 1 • • 1 1 2
After 9 Over
Pakistan 66/2 (RR: 7.33)
Ball-by-Ball: 1 2 1 2 1lb 1
After 8 Over
Pakistan 58/2 (RR: 7.25)
Ball-by-Ball: 3 1 W 1 1 4
OUT: Mohammad Hafeez c Vithanage b NLTC Perera 17
After 7 Over
Pakistan 48/1 (RR: 6.85)
After 6 Over
Pakistan 42/1 (RR: 7.00)
After 5 Overs
Pakistan 35/1 (RR: 7.00)
Ahmed Shehzad 21 (16b 3×4 0x6)
Mohammad Hafeez 8 (6b 1×4 0x6)
Mukhtar out after scoring just two runs in the 1.5 over
Pakistan XI: Ahmed Shehzad, Mukhtar Ahmed, Muhammad Hafeez, Shoaib Malik, Umar Akmal, Muhammad Rizwan, Shahid Afridi, Sohail Tanvir, Anwar Ali, Imad Wasim and Muahmmad Irfan.
Sri Lanka XI: Kusal Perera, T.M. Dilshan, Angelo Mathews, D de Silva, CK Kaugedera, KDK Vithanage, Siriwardana, Thisara Perera, JDF Vandersay, Lasith Malinga and Binura Fernando.
Pakistan skipper Shahid Afridi said it’s a good hard surface. Around 170-175 will be a very good total on this pitch, he added.
The big news from the centre is that Sarfraz Ahmed has been dropped.
While Sri Lankan captain said he would have bowled first anyway.
Umpires: Ranmore Martinesz (SRI) and Ruchira Palliyaguruge (SRI)
TV umpire: Raveendra Wimalasiri (SRI)
Match referee: Javagal Srinath (IND)