England captain Michael Vaughan and Andrew Strauss made 67 apiece as the touring side scored 280 for eight but the hosts reached their target with 17 balls to spare.
West Indies lead in the weather-disrupted series 2-1 with the final match scheduled for Barbados on Wednesday.
"Shivnarine Chanderpaul played a tremendous innings and Dwayne Bravo has only played two or three games but has got a lot of maturity," Lara said.
"We have a very exciting young team here but we need to be more consistent."
Just as in the fifth game on Saturday when West Indies successfully chased 282 for victory, England were left to rue missing out on a total in excess of 300 after slipping from 191 for three after 33 overs.
The tourists made a good start after being put into bat with Marcus Trescothick, who made 130 on Saturday, and Vaughan looking in good form.
But when Trescothick fell for 29 with the score on 57, England lost their impetus, allowing West Indies to slow the run-rate.
Vaughan and Strauss played sensibly as they added 84 for the second wicket.
Vaughan, still without a one-day international hundred, passed 50 for the seventh time but he was run out for 67 by a direct hit from Ricardo Powell.
Strauss worked the ball stylishly to record his first one-day international half-century but when he too had reached 67, including seven boundaries, he was trapped lbw by off spinner Chris Gayle, the pick of the West Indies bowlers with figures of two for 39 from 10 overs.
Andrew Flintoff hit 43 and Paul Collingwood 38 but the total never looked quite good enough, especially after Shivnarine Chanderpaul smashed one Darren Gough over for 15 on his way to his 29th one-day half-century.
Powell struck a quickfire 38 and Chanderpaul hit seven fours and one six before he was caught at short mid-wicket off Rikki Clarke's first ball for 63.
But with West Indies having raced to 113 for three in the 17th over, Lara and Ramnaresh Sarwan picked off singles at will.
Sarwan was deceived by Flintoff's slower ball to be bowled for 28, and Dwayne Smith, hero of Saturday's victory with 44 from 37 balls, struck three imperious boundaries before holing out to deep mid-wicket for 18.
Lara reached his 54th one-day international fifty with successive boundaries off Gough before falling for 57 top-edging a hook off Steve Harmison.
Dwayne Bravo (33 not out) and Ridley Jacobs (19 not out) steadied the hosts, however, seeing them comfortably to their target in the 48th over.
Vaughan admitted that his side's total was not competitive enough.
"We should have got a total of around 300 to 315 and that would have put them under more pressure," Vaughan said.
Scoreboard:
England
M.Trescothick b Rampaul 29
M.Vaughan run out (Powell) 67
A.Strauss lbw b Gayle 67
A.Flintoff c Chanderpaul b Bradshaw 43
P.Collingwood c Sarwan b Powell 38
C.Read run out (Dillon) 11
R.Clarke b Dillon 6
G.Batty b Gayle 1
D.Gough not out 3
S.Harmison not out 0
Extras (lb-3 w-10 nb-2) 15
Total (for eight wickets, 50 overs) 280
Fall of wickets: 1-57 2-141 3-199 4-251 5-258 6-273 7-276 8-276
Did not bat: J.Anderson
Bowling: Rampaul 8-0-54-1, Dillon 10-0-59-1, Bradshaw 10-0-61-1, Bravo 5-0-25-0, Smith 5-0-30-0, Gayle 10-0-39-2, Powell 2-0-9-1
West Indies
C.Gayle lbw b Gough 9
S.Chanderpaul c Batty b Clarke 63
R.Powell c sub (McGrath) b Batty 38
R.Sarwan b Flintoff 28
B.Lara c Gough b Harmison 57
D.Smith c Strauss b Batty 18
D.Bravo not out 33
R.Jacobs not out 19
Extras (lb-6 w-11) 17
Total (for six wickets, 47.1 overs) 282
Fall of wickets: 1-15 2-112 3-113 4-185 5-206 6-244
Did not bat: I.Bradshaw, R.Rampaul, M.Dillon
Bowling: Gough 8.1-0-67-1, Harmison 10-0-52-1, Anderson 4-0-27-0, Flintoff 9-0-55-1, Batty 9-0-40-2, Clarke 7-0-35-1
Result: West Indies won by four wickets
First match: Georgetown - England won by two wickets.
Second match: Port-of-Spain - abandoned as a draw due to rain
Third match: Port-of-Spain - abandoned as a draw due to rain
Fourth match: St George's, Grenada - abandoned as a draw due to rain
Fifth match: Castries, St Lucia - West Indies won by five wickets
Seventh match: May 5, Bridgetown, Barbados
