Morgan's 10th ODI hundred anchored England to a competitive 296-6 after being sent in to bat.
England won the first match by 45 runs at the same venue on Friday. West Indies' spinners, who out-bowled England's on Friday, are therefore likely to have a big role to play later in the day. The brace had taken Finn to 100 one-day wickets in 67 matches, the second fastest Englishman to hit three figures after Darren Gough and Stuart Broad (both 62); that these were also his first in one-day cricket for 18 months rather summed up the 27-year-old's enigmatic career to date.
But Root, superbly supported by Chris Woakes, who contributed an unbeaten 68 in a century stand, helped England to a four-wicket win which sees them take an unassailable 2-0 series lead into Thursday's final ODI in Barbados.
The resistance was then fully snuffed out by the 48th over when the returning Plunkett bowled Nurse and Buttler smartly ran out last man Gabriel. Woakes got to his second ODI 50 and brought the scores level emphatically by hitting a six.
The most impressive piece of work from England in the field though came courtesy of a sensational combination catch between Jason Roy and Sam Billings on the deep-midwicket boundary to dismiss Carlos Brathwaite.
The reunion was an anticlimax. Both Jos Buttler, dismissed for a duck - he now has just 81 runs from his last eight worldwide limited overs games - and Ben Stokes were out caught behind playing injudicious cut shots early in their innings and Moeen Ali was bowled by Nurse after playing back to a ball he should have been forward to.
Eoin Morgan, meanwhile, said that he would have bowled first any way and reckons the pitch might get better to bat on later.
He removed Mohammed and Jonathan Carter (39) before adding the scalp of Ashley Nurse to finish with three for 32.
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Although they took only one wicket between them, they were responsible for the rising desperation in the home side's ranks.
By then, there had been a second escape for Morgan - this time on 69, when Shai Hope failed to gather a stumping chance off Mohammed - and Stokes might also have gone but instead counted another leg-side six off Gabriel when Kraigg Brathwaite over-balanced beyond the rope and dropped the ball. There were three wickets from Liam Plunkett, to go with his four from the first game, and two apiece for Steven Finn and Adil Rashid.