Cameroonian defender Yves Ekawalla put the defending champions ahead after 19 minutes, but Osotspa equalised straight after the restart through Hiroyuki Yamamoto.
Ekawalla then scored at the wrong end to give the visitors the lead but Franck Ohandza equalised immediately with a spectacular overhead kick, before further strikes from Suchao Nutnum and Ohandza sealed all three points for Buriram.
Elsewhere, Chonburi's title bid took an early blow as they were held to a 1-1 at TOT.
Pipob On-mo had fired the visitors ahead in the 50th minute and things were looking fairly comfortable for them when TOT were reduced to ten men after striker Fofana Abib was sent off for dissent.
However, Diego Costa capitalised on a poor clearance from Chonburi defender Fode Bangaly to salvage an unlikely point for the hosts.
Police United condemned Thai Port to their fourth straight defeat of the season with a 1-0 victory.
Leandro dos Santos grabbed the only goal of the game after 73 minutes in a bad-tempered match that saw three players sent off.
Finally, newly-promoted BBCU recorded a creditable 1-1 draw with Army United. Adisak Ganu put Chula ahead after just eight minutes but Chaiwat Nakein netted in the 70th minute to steal a share of the spoils for his side.
On Sunday, Muang Thong United will be looking to reclaim top spot in their game against Chainat, while Bangkok Glass are in action against Pattaya United.
Esan United and Wuachon United go head to head at the Ubon Ratchathani Stadium, BEC Tero Sasana entertain Chiangrai United, while Samut Songkhram take on TTM Chiangmai.
Saturday's Thai Premier League Results
Buriram United 4-2 Osotspa Saraburi
TOT 1-1 Chonburi
Thai Port 0-1 Police United
Army United 1-1 BBCU
Sunday's Thai Premier League Fixtures
Chainat vs Muang Thong United
Bangkok Glass vs Pattaya United
Esan United vs Wuachon United
BEC Tero Sasana vs Chiangrai United
Samut Songkhram vs TTM Chiangmai