COLOMBO: Umar Akmal smashed an unbeaten 102 off 72 balls as Pakistan won the fourth one-dayer by 146 runs on Friday to record their first win on a dismal tour of Sri Lanka.

Umar's maiden international century and a dogged 89 from skipper Younus Khan lifted Pakistan to 321-5 after the tourists elected to bat in the day-night match at the Premadasa stadium.

Seamer Rao Iftikhar then grabbed 5-30 as Sri Lanka were shot out for 175 in 36.1 overs, handing Pakistan a badly-needed win after they were beaten 2-0 in the Test series and lost the first three one-dayers.

The fifth and final match will be played at the same venue on Sunday.

Umar, 19, younger brother of the team's wicket-keeper Kamran Akmal, pounded four sixes and five boundaries in only his third international and was declared the man of the match.

Younus stayed rock-solid at the other end as Umar punished the wayward Sri Lankan attack during a fifth-wicket partnership of 176 runs after Pakistan slipped to 130-4.

Sri Lanka appeared to make light of the daunting target when they moved to 101-1 in the 16th over, before losing their last nine wickets for 74 runs.

Left-handed opener Upul Tharanga top-scored with 80 off 89 balls and skipper Kumar Sangakkara made 39, but none of the other top order batsmen delivered.

Spinners Shahid Afridi and Saeed Ajmal supported Iftikhar with two wickets each.

"It's a relief to win finally," said Younus at the presentation ceremony. "We are normally slow starters, but we have been too slow on this tour.

"Hats off to Umar and Iftikhar. They really made us proud today."

Sangakkara said a target of 321 could not be chased without big partnerships, which Sri Lanka did not have.

"I don't think complacency was the problem," he said. "The problem was we gave them 320. We have got to make sure we bowl a lot better to our fields.

"Umar finished things off very well for Pakistan. But we need to keep our chins up and come back strongly in the next match."

Earlier, Pakistan made a sound start as Imran Nazir, playing for the first time in the series, hit 23 in a first-wicket stand of 61 with Kamran Akmal by the 10th over.

Kamran then put on 45 for the second wicket with Younus to lift Pakistan to 106-1, before another middle-order collapse saw three wickets fall for 24 runs.

Leg-spinner Malinga Bandara, himself making his first appearance in the series, bowled Kamran and trapped Misbah-ul-Haq leg-before to finish with two for 44 in 10 overs.

Lasith Malinga went for 79 runs in his 10 wicketless overs, while fellow paceman Thilan Thushara took two wickets for 74 runs.

Sri Lanka rested three frontline bowlers, Muttiah Muralitharan, Nuwan Kulasekara and Dilhara Fernando, and replaced them with Ajantha Mendis, Bandara and Malinga.

Pakistan were forced to leave out the injured duo of Umar Gul and Abdul Razzaq and also dropped Nasir Jamshed and Fawad Alam.

They were replaced by Nazir, Mohammad Yousuf, Misbah and Iftikhar.