Shahid Afridi starred with both bat and ball, hitting a robust 75 to help Pakistan reach 200 before taking 4-35 to dismiss Sri Lanka for 174 in 45.2 overs.
The fifth and final match will be played in Abu Dhabi on Wednesday.
Complete scoreboard:
Pakistan
Mohammad Hafeez c Chandimal b Prasanna 27
Imran Farhat c Sangakkara b Fernando 10
Younis Khan c Mendis b Fernando 18
Misbah-ul Haq run out 16
Shoaib Malik lbw b Mendis 2
Umar Akmal lbw b Mendis 2
Shahid Afridi c Sangakkara b Perera 75
Sarfraz Ahmed lbw b Prasanna 10
Saeed Ajmal lbw b Fernando 20
Umar Gul b Malinga 7
Aizaz Cheema not out 3
Extras: (lb2, w8) 10
Total: 200
Fall of wickets: 1-18 (Farhat), 2-57 (Hafeez), 3-62 (Younis), 4-69 (Malik), 5-71 (Akmal), 6-97 (Misbah), 7-120 (Ahmed), 8-181 (Afridi), 9-191 (Ajmal).
Bowling: Malinga 9.3-0-38-1 (w2), Perera 10-1-36-1 (w2), Fernando 10-3-26-3, Mendis 9-0-40-2, Prasanna 10-1-55-2 (w4), Dilshan 1-0-3-0
Overs: 49.3
Sri Lanka
U. Tharanga c Younis b Cheema 16
T. Dilshan c Ahmed b Cheema 11
K. Sangakkara b Afridi 58
D. Chandimal b Hafeez 11
M. Jayawardene c Hafeez b Afridi 55
A. Mathews c Ahmed b Ajmal 0
J. Mendis lbw b Afridi 2
T. Perera c Akmal b Afridi 7
S. Prasanna c and b Afridi 0
L. Malinga lbw b Ajmal 4
D. Fernando not out 0
Extras: (lb3, nb1, w6) 10
Total: 174
Fall of wickets: 1-18 (Tharanga), 2-37 (Dilshan), 3-53 (Chandimal), 4-155 (Sangakkara), 5-156 (Mathews), 6-161 (Mendis), 7-168 (Jayawardene), 8-168 (Prasanna), 9-174 (Malinga)
Bowling: Gul 6-0-19-0, Cheema 8-0-48-2 (w2), Hafeez 8-1-23-1, Malik 5-1-17-0 (nb1, w2), Ajmal 9-1-29-2 (w1), Afridi 9.2-0-35-5 (w1)
Overs: 45.2
Result: Pakistan won by 26 runs
Toss: Pakistan
Umpires: Richard Illingworth (ENG) and Zameer Haider (PAK)
Tv umpire: Marias Erasmus (RSA)
Match referee: Andy Pycroft (ZIM)