The improvement in Milinda Siriwardana's bowling may allow Sri Lanka to explore new combinations in their ODI side, vice-captain Lahiru Thirimanne said. It was largely Siriwardana's batting that saw him elevated to the national team, but both Thirimanne and captain Angelo Mathews have now spoken of Siriwardana's growing skill with the ball.
Siriwardana has three wickets at an average of 26.33 in the five ODIs he has played so far. He was more impressive in the recent Test series against West Indies, in which he claimed seven wickets at 17.71. Tillakaratne Dilshan has provided a part-time spin option for Sri Lanka, but if both he and Siriwardana play, the hosts will have an offspinner and a left-arm spinner in their top seven.
"I think the main thing we've been impressed with is Milinda's bowling," Thirimanne said. "We all knew he has got talent with the bat, but he has improved a lot in his bowling. It's a big advantage when it comes to the one-day side. We haven't had a spinning allrounder in the last few years."
In addition to Dilshan and Siriwardana, Sri Lanka also have frontline spinners Ajantha Mendis, Sachithra Senanayake and Jeffrey Vandersay in the squad. West Indies had lost 27 wickets to spin during the Test series, but Thirimanne expected stiffer resistance in the ODIs.
"We are hopeful that our spinners and slow bowlers will give us the advantage," he said. "But we can't take the West Indies team lightly. They didn't play the Tests well, but the one day team is quite strong overall. There are a lot of players who can change a match in that team."
Sri Lanka have three uncapped players in their squad, two of whom may play in the first ODI. Dinesh Chandimal's one-match suspension may allow both Shehan Jayasuriya and Danushka Gunathilaka to enter the XI.
"I think we'll need to work out what our best combination is during this series," Thirimanne said. "After the World Cup a lot of seniors left. We then played the Pakistan team, and if you take our batting line-up or our bowling line-up, we aren't that settled. This series will help figure out a settled side."
Thirimanne himself had been dropped from the second Test in Colombo, after a long sequence of modest scores in that format. He will bat at No.3 on Sunday, however, having averaged 40.81 in ODIs this year.
"I wasn't successful in Tests. But if you look at my record, I've played very differently in Tests and one-dayers. I've done well in ODIs, but haven't been able to replicate that in Tests. I don't know why that is, but I'm expecting to go to the middle and score runs. There are times when scoring runs is difficult, but the best thing to do is enjoy the game."

Andrew Fidel Fernando is ESPNcricinfo's Sri Lanka correspondent. @andrewffernando