The West Indies entered Friday’s fourth and final day on 119-3 off 31.5 overs, a deficit of 313 runs.
Jordan Johnson, who entered the day unbeaten on 54, carried on to make a brilliant 149 off 207 balls including 11 fours and two sixes. Johnson also hit a century in the ODI series.
Steven Wedderburn entered the day on 28 and eventually made 41 while Nathan Edward contributed 36 as the West Indies were eventually bowled out for 309 in 89.5 overs.
Vihas Thewmika took 6-78 off 28.5 overs while Vishwa Lahiru took 3-61 off 24 overs for the hosts.
Sri Lanka then reached 122-4 in their second innings before play was called off and the spoils were shared.
Ravishan Nethsara hit an even 50.
The teams will now turn their attention to the second match beginning on Monday.
Sri Lanka first dismissed the young West Indians for 127 in 36.4 overs after the tourists won the toss and chose to bat.
Left-hander Jordan Johnson followed up his 149 in the last game with a 49-ball 52 including six fours and two sixes while openers Stephan Pascal and Steven Wedderburn hit 28 and 24, respectively.
Vihas Thewmika led the way with the ball for Sri Lanka with 5-43 from 11.4 overs while Malsha Tharupathi took 3-16 from five overs.
Sri Lanka then reached 191-4 off 51 overs at stumps.
Rusanda Gamage was the top scorer with 58 from 52 balls including 10 fours while Ravishan de Silva hit 43 and Pulindu Perera made 41.
Isai Thorne, Deshawn James and Nathan Sealy took the wickets.
The West Indies ended Thursday’s third day on 119-3 from 31.5 overs replying to Sri Lanka’s massive 432-8 declared.
Jordan Johnson has led the way for the young West Indians so far with an unbeaten 54 while his Jamaican countryman, Steven Wedderburn, is the other not out batsman on 28.
Vishwa Lahiru has picked up 2-22 in 11 overs for the hosts.
Resuming from their overnight score of 251-8 with Johnson on 133 and Tamarie Redwood yet to score, the West Indies U19s, added 26 to their total, bowled out for 277. Johnson added 24 of the runs added but Redwood was run out for two and Deshawn James run out without scoring, leaving Johnson on 157 not out.
Needing just 79 for victory, Sri Lanka 81-3 from just 18.4 overs to secure victory.
Sineth Jayawardene top scored with 30 while Rusanda Gamage was not out on 21 at the end with Ravishan De Silva on 17 at the other end. The pair added 42 runs for the fourth wicket, after the West Indies threatened briefly to have the hosts in a spot of bother at 39-3.
Isai Thorne, 1-29 and Tarrique Edward, 1-16, were the wicket takers for the West Indies in the losing effort.
The West Indies U19 lost but Johnson did not come away empty-handed. For his scores of 149, 52 and 157 not out, he was named Player of the Series.
Scores: West Indies U19 127 and 277 v Sri Lanka U19 326 and 81-3. Sri Lanka winning by seven wickets.
Only 38 overs were possible on the day after the hosts won the toss and decided to bat first.
Opener Pulindu Perera, who hit 155 in the third ODI last week, followed that up with a 66-ball 71 including eight fours and two sixes.
Captain Sineth Jayawardene, who opened the batting as well, made a run-a-ball 34 while Ravishan Nethsara ended the day 31*.
Tarrique Edward, Nathan Sealy and Isai Thorne are the West Indian wicket-takers, so far.
