The West Indies offered a collective sigh of relief, after Devon Smith and Marlon Samuels hit half-centuries to set things up, then Dwayne Smith and Darren Sammy helped them formalise a 15-run win.
West Indies successfully defended a target of 209, when they restricted England to 193 for seven in their allocation of 20 overs.
It was the West Indies’ first win in a match against England on the tour, following a 0-3 defeat in the preceding four-Test series, and earned the visitors a 1-0 lead in the two-match series.
Dwayne Smith was the most successful West Indies bowler with three wickets for 24 runs from his allotment of four overs, and Darren Sammy supported with two for 37 for his four overs.
England captain Paul Collingwood top-scored for his side with an undefeated 79 off 41 balls and earned the Man-of-the-Match award.
Devon Smith had led the West Indies batting with a fluent 61 from 34 balls, Marlon Samuels struck 51 off 26 balls including one of the biggest sixes ever hit at the Oval, and Shivnarine Chanderpaul made 41 from 26 balls, as West Indies posted 208 for eight from their 20 overs.
James Anderson and England newcomer Dmitri Mascarenhas snared two wickets apiece.
West Indies then bowled and fielded with purpose to leave England on 101 for six in the 13th over, but a stand of 91 between Collingwood, in his first match as England limited-overs captain, and Michael Yardy revived the home team’s chances.
Ravi Rampaul, playing his first international match for three years, bowled a tight penultimate over that only cost seven runs leaving England to get 23 from the last six balls.
Dwayne Bravo had been advised not to bowl because of a dodgy ankle, but he ignored the physio’s advice, insisted that he could, and West Indies captain Chris Gayle entrusted him with the visitors’ “life”, and he again put a smile on West Indies faces with a final over that also cost seven.
In the chase, West Indies appeared under pressure, when openers Alastair Cook and Matt Prior put on 40 for the first wicket inside the first five over.
Dwayne Smith however, removed them both in the space of five balls in his first over, when he had Cook caught at point for 15, and Prior caught in the deep for 25 to leave England 48 for two.
Smith and Sammy then tightened the screws, as a cluster of wickets between the eighth and 13th overs left England’s hopes teetering on the edge until their captain turned things around.
Sammy bowled Jonathan Trott for nine, Kevin Pietersen was run out for 16 going for two when he failed to beat Dwayne Smith’s throw from the cover boundary to Samuels at the bowlers’ end, Owais Shah was adjudged lbw to Smith for seven, and Mascarenhas was caught at short third man off Sammy for two.
Earlier, Gayle was bowled off the inside edge for five in second, but Devon Smith and Chanderpaul put West Indies in control with a stand of 84 for the second wicket.
When Chanderpaul was caught at deep mid-wicket off Mascarenhas, Samuels arrived and he played his natural game, despite wickets tumbling at the other end.
He added a crucial 59 for the fifth wicket with Denesh Ramdin, who made 24, before they were dismissed in the space of five balls leaving the tailenders to carry West Indies over the 200-run hump.
The second match of the series will be contested tomorrow at the same venue.