The 1996 World champions needed two wins in the five- match series to secure a place in the ICC's pinnacle 50-over event, which will take place from May 30 to July 15 in the United Kingdom. The top seven ODI sides apart from host England as on 30 September qualify directly.
But with India taking a 4-0 lead, Sri Lanka will now have to wait for the West Indies to lose at least one of their upcoming matches to be able to clinch that berth.
The Windies will be able to overtake Sri Lanka in such a scenario since they can also reach 88 points and edge Sri Lanka on decimal points if they win their upcoming six matches - one against Ireland on 13 September and all ODIs of a five- match series against England from September 19 to 29.
In case Sri Lanka lose the series 5-0, the Windies will be able to overtake them by beating Ireland and winning either all five matches against England or the last four matches for a 4-1 series win.
The World Cup Qualifier 2018 will feature the bottom four sides from the ICC ODI team rankings, the top four sides from the World Cricket League Championship and the top two sides from the World Cricket League.
The top two sides from the World Cup Qualifier will complete the 10-team line-up for the World Cup 2019.