Although both teams have already made it to the main tournament starting on Sunday, the stakes will be high in the day-night match at the Brabourne stadium here on Saturday.
The winner will top the qualifiers and be placed with South Africa, Pakistan and New Zealand in Group B of the main tournament.
The loser goes to group A that has world champions Australia, England and hosts India.
Both teams breezed past minnows Zimbabwe and Bangladesh as expected, but Sri Lanka are worried by the high number of extras they conceded in the two games.
The Sri Lankans gave away 21 wides and eight no-balls in their first match against Bangladesh in Mohali and 19 wides and seven no-balls against Zimbabwe in Ahmedabad.
That added up to 9.1 additional overs, a luxury captain Mahela Jayawardene said the team can ill-afford against the established teams.
"We are working on correcting this," he said. "The bowlers were obviously a bit rusty since they had not played one-day cricket since June."
Sri Lanka were denied useful one-day practice at home in August when South Africa abandoned a tri-series also featuring India due to security reasons, following a bomb blast near their team hotel in Colombo.
A hurriedly arranged three-match series against India was rained off.
Sri Lanka showed their class by beating Bangladesh by 37 runs in their opening qualifying match and then thumped Zimbabwe by 144 runs.
Young opener Upul Tharanga, a 21-year-old survivor of the killer tsunami in December 2004 when his home in Sri Lanka's west coast was washed away, led the way with centuries in both matches.
Sri Lanka have won eight of their last 11 matches against the West Indies, but suffered a 33-run defeat in their last game in Colombo in 2005.
"The West Indies are playing very well and we will have to be at our best to win," said Jayawardene. "No match will be easy from now on."
The West Indians have so far lived up to their captain Brian Lara's desire to crush the opposition, swamping Zimbabwe by nine wickets before thrashing Bangladesh by 10 wickets.
Lara, clearly enjoying his third term as captain, wants to build on the momentum.
"The win on Saturday is very important for us as we'd love to qualify as the number one side and move on. We'd also love to continue the momentum," he said.
Lara said Sri Lanka will also be keen on winning because no side wanted to suffer a defeat going into the main stage of the tournament.
"Both teams are going to be very competitive," he said. "We are going to go strongly for a win because I think three wins on a trot going into the second stage is definitely a positive."
Lara will once again be looking for a blistering start from opener Chris Gayle, who made 41 against Zimbabwe and smashed an unbeaten 104 against Bangladesh.
The one-sided wins in the previous two games that has left his batsmen short of match practice does not worry Lara.
"If Chris (Gayle) and (Shivnarine) Chanderpaul are the only two to bat on Saturday, then this is great for us," he said.
The wicket at the Brabourne stadium seems to be a batting friendly one but with the match being a day-night affair, the teams taking into consideration of the dew factor in the evening, would like to bat second for this very reason.
Sri Lanka: Mahela Jayawardene (c), Marvan Atapattu, Malinga Bandra, T Dilshan, Dilhara Fernando, Sanath Jayasuriya, C Kapugedera, F Maharoof, Lasith Malinga, Muttiah Muralitharan, Ruchira Perera, Kumar Sangakkara (wk), Upal Tharanga and Chaminda Vaas
West Indies: Brian Lara (capt), Ramnaresh Sarwan, C S Baugh (wk), Ian Bradshaw, D Bravo, S Chanderpaul, Corry Collymore, Fidel Edwards, Chris Gayle, Wavell Hinds, Runako Morton, Marlon Samuels, D Smith and J Taylor.