Essex 210 for 4 (Browne 69, Pettini 57, Westley 53) beat Hampshire 209 (Dawson 85, Smith 63, Topley 4-26, Porter 3-39) by six wickets
The top three all collected half centuries as Essex chased down 209 simply and moved above Hampshire in Group B of the Royal London Cup. Reece Topley, 4 for 26, was the pick of the bowlers as Hampshire had two collapses.
After losing the toss and bowling Hampshire out for 209, Essex openers Pettini and Browne sprayed the home side's attack around the Ageas Bowl.
Browne, on just his fifth List A appearance, had previously only scored nine format runs but freely spread the ball around - reaching fifty in 47 balls, including nine boundaries. He departed for 69, bowled by former team-mate Liam Dawson, after a 122-run opening stand.
Pettini batted slower than his partner but reached his half century in 74 balls as Essex never got out of first gear in an easy chase. The batsman got Essex to within 43 within victory before he was stumped off Will Smith
Westley got himself in quickly and smashed Mason Crane for back-to-back boundaries and completed a trio of top three fifties, from 50 balls.
Westley charged Crane to be stumped by Wheater and Jesse Ryder was bowled but Ravi Bopara and Ryan ten Doeschate saw the visitors home with 48 balls to spare.
Earlier the home side had rushed to 31 in six overs before Michael Carberry was caught cutting to point in a staccato 6 from 19.
The next delivery, opening partner Jimmy Adams was out in odd circumstances, as he clipped his own wicket with his trailing foot while attempting to steer down the leg side after a lively 23.
Vince was bowled by Jamie Porter two overs later and three balls later Wheater, against his former county was castled in an instant replay of the skippers wicket.
Hampshire had scored just five runs in 19 balls for the four early wickets to leave them up against it.
Joe Gatting and Dawson attempted to add some much needed runs as the pair put on 32 runs, with the former top edging over the top four for but Topley had his revenge next ball when he fired straight to Bopara at mid-on.
Where Gatting failed Smith succeeded, moving past 50 for the sixth wicket with Dawson from 71 balls. Dawson scored his 2000th List A run before he reached a ninth format fifty in 69 balls in a classy knock.
Smith followed his partner to the landmark in six balls fewer as the Hampshire middle order rebuilt after a stodgy start The duo collected a 100-run partnership from 123 balls before Smith was caught behind attempting to cut to end the 124 run stand.
That wicket started a 32-ball collapse where Hampshire fell from 192 for 5 to 209 all out. Chris Wood was run out by almost the length of the pitch in a horrible mix up with Dawson before Topley comprehensively bowled Crane.
Dawson, was dismissed top edging a hook short to Browne at short fine leg - for a magnificent 85 - before Fidel Edwards was the final man to go when he mistimed a pull to Pettini to give Topley his fourth wicket.