MIRPUR: Ajantha Mendis and Thisara Perera snared six wickets and Kumar Sangakkara hit a half century as Sri Lanka reached the Asia Cup final with a 129-run win over Afghanistan on Monday.

Mendis took 3-11 off his unorthodox spin and Perera bowled a miserly 10-over spell for his 3-29 to get Afghanistan out for 124 with more than 11 overs to spare after Sangakkara's 76 off 102 balls had lifted Sri Lanka to 253-6.

After their third successive victory, Sri Lanka booked Saturday's final berth with 13 points, including a bonus point after their emphatic win on Monday.

Captain Mohammad Nabi top scored for Afghanistan with 37 but in a dramatic collapse the team lost its last five wickets for only three runs.

“It was a very important game for us because we had to book our place in the final,” said Sri Lanka captain Angelo Mathews, who scored a vital unbeaten 45 off 41 balls to propel the total.

“They have a very good bowling attack and our batsmen found it hard, it was a slow pitch, too.”

Afghanistan had made its mark in its maiden appearance at the biennial tournament when it defeated host Bangladesh, but the team's batsmen struggled to negotiate both seam and spin of Sri Lanka on a slow wicket.

Asghar Stanikazi showed a bit of spark by hitting five boundaries in his 27 before the innings crumbled against Perera and Mendis.

Nabi and Najibullah Zadran (11) put on 48 runs for the sixth wicket stand before spinner Chaturanga de Silva (2-29) and Mendis polished off the innings in quick time.

“We bowled brilliantly in the first 35 overs and Sangakkara played very well,” Nabi said. “We started well with the bat, but then Mendis bowled brilliantly.”

Earlier, Sangakkara, who made a half century against Pakistan and a century against India in Sri Lanka's previous two victories, held the innings together by hitting six fours and a six against some tidy bowling.

“There is nothing guaranteed in cricket, you can be in fine form, but it takes only one ball for you to get out, so you have to enjoy while it goes well,” Sangakkara said.

Afghanistan had restricted Sri Lanka at 171-5 by the 40th over when Dinesh Chandimal (28) was clean bowled and Sangakkara was run out in successive overs before Mathews put on 69 runs with Thisara Perera off 49 balls.

“It was a tough wicket to bat on, so we had to spend some time to build a foundation,” Sangakkara said. “You can't take anything for granted, the Afghan team played very well, they exploited the pitch very well.”

Sri Lanka's top order also struggled on a dual paced wicket after Mathews won the toss and elected to bat first.

Left-arm fast bowler Shapoor Zadran had Lahiru Thirimanne's leg stump uprooted off a delivery which swung in on the left-hander and Kusal Perera played onto Ashraf's delivery back onto his stumps.

Offspinner Nabi conceded only seven runs in his first four overs and also deployed eight bowlers within the first 26 overs that kept the scoring rate under check.

Jayawardene's poor run of form continued when he was well caught by Nabi at mid-on before Sangakkara and Chandimal put on 74 runs off 93 balls to put the innings back on track.

Afghanistan struck through left-arm spinner Hamza Hotak in the second batting powerplay when he had Chandimal clean bowled.

Sangakkara, who was dropped on 62 by Dawlat Zadran off his own bowling and wicketkeeper Mohammad Shahzad missed out on a run out when the left-hander had reached 75, was run out in a mixup with Mathews as Afghanistan hit twice in space of one run.

Mathews ensured Sri Lanka avoided more hiccups by hitting four boundaries in his 41-ball knock and get the total past the 250 mark.

Zadran had to be taken out of the attack for bowling second beamer in the innings in the last over before Nabi completed his over.