Masahiro Wada's Chonburi side never looked in danger at the Chonburi Municipality Stadium as they opened the campaign in style on Saturday.
The hosts had a two-goal cushion at half-time thanks to Thiago Cunha's brace, the first of which came from the penalty spot.
Chonburi's dominance continued in the second period as Anderson dos Santos added a third with 15 minutes remaining before Police United were reduced to 10 men in the 88th minute when Saranyu Intaraat was sent off.
And the visitors' misery was compounded deep into injury time when Therdsak Chaiman added a fourth.
At Thunder Castle Stadium, Buriram started the defence of their title with a straightforward 3-0 triumph over Songkhla United.
Javier Patino opened the scoring after just nine minutes before Leonel Altobelli added a second 13 minutes from time. A second from Patino late in the 82nd minute completed the win.
Muang Thong United, last season's runners-up, needed a late comeback to defeat Chainat 2-1 at SCG Stadium.
Panuwat Failai put the hosts ahead in the 21st minute, but Chainarong Tathong levelled with just 15 minutes left. And the home side completed the turnaround in the 91st minute when Mario Gjurovski bagged from the penalty spot.
Elsewhere on Saturday, Teeratep Winothai's brace handed 10-man Bangkok Glass a 2-0 win at Chiangrai United, while Suphanburi fell to a 2-1 loss at home against Ratchaburi.
On Sunday, the games involving Air Force Central and TOT and Samut Songkhram and BEC Tero Sasana finished 0-0, while Singhtarua and PTT Rayong played out a 1-1 draw.
Goals from Goran Jerkovic and Mongkol Tossakai helped Army United to a 2-1 victory over Bangkok United, while a solitary Jeferson goal saw Osotspa win 1-0 at Sisaket.
